17 files changed, 5266 insertions, 0 deletions

diff --git a/src/lib-ssl-iostream/Makefile.am b/src/lib-ssl-iostream/Makefile.am
new file mode 100644
index 0000000..5aaea5d
--- /dev/null
+++ b/src/lib-ssl-iostream/Makefile.am
@@ -0,0 +1,61 @@
+noinst_LTLIBRARIES = libssl_iostream.la
+
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+
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+	-I$(top_srcdir)/src/lib \
+	-I$(top_srcdir)/src/lib-test \
+	-DMODULE_DIR=\""$(moduledir)"\"
+
+if BUILD_OPENSSL
+module_LTLIBRARIES = libssl_iostream_openssl.la
+
+libssl_iostream_openssl_la_LDFLAGS = -module -avoid-version
+libssl_iostream_openssl_la_LIBADD = $(SSL_LIBS)
+libssl_iostream_openssl_la_SOURCES = \
+	dovecot-openssl-common.c \
+	iostream-openssl.c \
+	iostream-openssl-common.c \
+	iostream-openssl-context.c \
+	istream-openssl.c \
+	ostream-openssl.c
+endif
+
+libssl_iostream_la_SOURCES = \
+	iostream-ssl.c \
+	iostream-ssl-context-cache.c \
+	iostream-ssl-test.c
+
+noinst_HEADERS = \
+	dovecot-openssl-common.h
+
+headers = \
+	iostream-openssl.h \
+	iostream-ssl.h \
+	iostream-ssl-private.h \
+	iostream-ssl-test.h
+
+pkginc_libdir=$(pkgincludedir)
+pkginc_lib_HEADERS = $(headers)
+
+if BUILD_OPENSSL
+test_libs = \
+	$(module_LTLIBRARIES) \
+	$(noinst_LTLIBRARIES) \
+	../lib-test/libtest.la \
+	../lib/liblib.la
+
+test_iostream_ssl_SOURCES = test-iostream-ssl.c
+test_iostream_ssl_LDADD = $(test_libs) $(SSL_LIBS) $(DLLIB)
+test_iostream_ssl_DEPENDENCIES = $(test_libs)
+
+test_programs = \
+	test-iostream-ssl
+
+noinst_PROGRAMS = $(test_programs)
+
+check-local:
+	for bin in $(test_programs); do \
+	  if ! $(RUN_TEST) ./$$bin; then exit 1; fi; \
+	done
+endif
diff --git a/src/lib-ssl-iostream/Makefile.in b/src/lib-ssl-iostream/Makefile.in
new file mode 100644
index 0000000..3929741
--- /dev/null
+++ b/src/lib-ssl-iostream/Makefile.in
@@ -0,0 +1,970 @@
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+maintainer-clean-generic:
+	@echo "This command is intended for maintainers to use"
+	@echo "it deletes files that may require special tools to rebuild."
+clean: clean-am
+
+clean-am: clean-generic clean-libtool clean-moduleLTLIBRARIES \
+	clean-noinstLTLIBRARIES clean-noinstPROGRAMS mostlyclean-am
+
+distclean: distclean-am
+		-rm -f ./$(DEPDIR)/dovecot-openssl-common.Plo
+	-rm -f ./$(DEPDIR)/iostream-openssl-common.Plo
+	-rm -f ./$(DEPDIR)/iostream-openssl-context.Plo
+	-rm -f ./$(DEPDIR)/iostream-openssl.Plo
+	-rm -f ./$(DEPDIR)/iostream-ssl-context-cache.Plo
+	-rm -f ./$(DEPDIR)/iostream-ssl-test.Plo
+	-rm -f ./$(DEPDIR)/iostream-ssl.Plo
+	-rm -f ./$(DEPDIR)/istream-openssl.Plo
+	-rm -f ./$(DEPDIR)/ostream-openssl.Plo
+	-rm -f ./$(DEPDIR)/test-iostream-ssl.Po
+	-rm -f Makefile
+distclean-am: clean-am distclean-compile distclean-generic \
+	distclean-tags
+
+dvi: dvi-am
+
+dvi-am:
+
+html: html-am
+
+html-am:
+
+info: info-am
+
+info-am:
+
+install-data-am: install-moduleLTLIBRARIES install-pkginc_libHEADERS
+
+install-dvi: install-dvi-am
+
+install-dvi-am:
+
+install-exec-am:
+
+install-html: install-html-am
+
+install-html-am:
+
+install-info: install-info-am
+
+install-info-am:
+
+install-man:
+
+install-pdf: install-pdf-am
+
+install-pdf-am:
+
+install-ps: install-ps-am
+
+install-ps-am:
+
+installcheck-am:
+
+maintainer-clean: maintainer-clean-am
+		-rm -f ./$(DEPDIR)/dovecot-openssl-common.Plo
+	-rm -f ./$(DEPDIR)/iostream-openssl-common.Plo
+	-rm -f ./$(DEPDIR)/iostream-openssl-context.Plo
+	-rm -f ./$(DEPDIR)/iostream-openssl.Plo
+	-rm -f ./$(DEPDIR)/iostream-ssl-context-cache.Plo
+	-rm -f ./$(DEPDIR)/iostream-ssl-test.Plo
+	-rm -f ./$(DEPDIR)/iostream-ssl.Plo
+	-rm -f ./$(DEPDIR)/istream-openssl.Plo
+	-rm -f ./$(DEPDIR)/ostream-openssl.Plo
+	-rm -f ./$(DEPDIR)/test-iostream-ssl.Po
+	-rm -f Makefile
+maintainer-clean-am: distclean-am maintainer-clean-generic
+
+mostlyclean: mostlyclean-am
+
+mostlyclean-am: mostlyclean-compile mostlyclean-generic \
+	mostlyclean-libtool
+
+pdf: pdf-am
+
+pdf-am:
+
+ps: ps-am
+
+ps-am:
+
+uninstall-am: uninstall-moduleLTLIBRARIES uninstall-pkginc_libHEADERS
+
+.MAKE: check-am install-am install-strip
+
+.PHONY: CTAGS GTAGS TAGS all all-am am--depfiles check check-am \
+	check-local clean clean-generic clean-libtool \
+	clean-moduleLTLIBRARIES clean-noinstLTLIBRARIES \
+	clean-noinstPROGRAMS cscopelist-am ctags ctags-am distclean \
+	distclean-compile distclean-generic distclean-libtool \
+	distclean-tags distdir dvi dvi-am html html-am info info-am \
+	install install-am install-data install-data-am install-dvi \
+	install-dvi-am install-exec install-exec-am install-html \
+	install-html-am install-info install-info-am install-man \
+	install-moduleLTLIBRARIES install-pdf install-pdf-am \
+	install-pkginc_libHEADERS install-ps install-ps-am \
+	install-strip installcheck installcheck-am installdirs \
+	maintainer-clean maintainer-clean-generic mostlyclean \
+	mostlyclean-compile mostlyclean-generic mostlyclean-libtool \
+	pdf pdf-am ps ps-am tags tags-am uninstall uninstall-am \
+	uninstall-moduleLTLIBRARIES uninstall-pkginc_libHEADERS
+
+.PRECIOUS: Makefile
+
+
+@BUILD_OPENSSL_TRUE@check-local:
+@BUILD_OPENSSL_TRUE@	for bin in $(test_programs); do \
+@BUILD_OPENSSL_TRUE@	  if ! $(RUN_TEST) ./$$bin; then exit 1; fi; \
+@BUILD_OPENSSL_TRUE@	done
+
+# Tell versions [3.59,3.63) of GNU make to not export all variables.
+# Otherwise a system limit (for SysV at least) may be exceeded.
+.NOEXPORT:
diff --git a/src/lib-ssl-iostream/dovecot-openssl-common.c b/src/lib-ssl-iostream/dovecot-openssl-common.c
new file mode 100644
index 0000000..76f98bc
--- /dev/null
+++ b/src/lib-ssl-iostream/dovecot-openssl-common.c
@@ -0,0 +1,132 @@
+/* Copyright (c) 2016-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "randgen.h"
+#include "dovecot-openssl-common.h"
+
+#include <openssl/ssl.h>
+#include <openssl/engine.h>
+#include <openssl/rand.h>
+
+static int openssl_init_refcount = 0;
+static ENGINE *dovecot_openssl_engine;
+
+#ifdef HAVE_SSL_NEW_MEM_FUNCS
+static void *dovecot_openssl_malloc(size_t size, const char *u0 ATTR_UNUSED, int u1 ATTR_UNUSED)
+#else
+static void *dovecot_openssl_malloc(size_t size)
+#endif
+{
+	/* this may be performance critical, so don't use
+	   i_malloc() or calloc() */
+	void *mem = malloc(size);
+	if (mem == NULL) {
+		i_fatal_status(FATAL_OUTOFMEM,
+			"OpenSSL: malloc(%zu): Out of memory", size);
+	}
+	return mem;
+}
+
+#ifdef HAVE_SSL_NEW_MEM_FUNCS
+static void *dovecot_openssl_realloc(void *ptr, size_t size, const char *u0 ATTR_UNUSED, int u1 ATTR_UNUSED)
+#else
+static void *dovecot_openssl_realloc(void *ptr, size_t size)
+#endif
+{
+	void *mem = realloc(ptr, size);
+	if (mem == NULL) {
+		i_fatal_status(FATAL_OUTOFMEM,
+			"OpenSSL: realloc(%zu): Out of memory", size);
+	}
+	return mem;
+}
+
+#ifdef HAVE_SSL_NEW_MEM_FUNCS
+static void dovecot_openssl_free(void *ptr, const char *u0 ATTR_UNUSED, int u1 ATTR_UNUSED)
+#else
+static void dovecot_openssl_free(void *ptr)
+#endif
+{
+	free(ptr);
+}
+
+void dovecot_openssl_common_global_ref(void)
+{
+	if (openssl_init_refcount++ > 0)
+		return;
+
+	/* use our own memory allocation functions that will die instead of
+	   returning NULL. this avoids random failures on out-of-memory
+	   conditions. */
+	if (CRYPTO_set_mem_functions(dovecot_openssl_malloc,
+				     dovecot_openssl_realloc, dovecot_openssl_free) == 0) {
+		/*i_warning("CRYPTO_set_mem_functions() was called too late");*/
+	}
+
+	SSL_library_init();
+	SSL_load_error_strings();
+	OpenSSL_add_all_algorithms();
+}
+
+bool dovecot_openssl_common_global_unref(void)
+{
+	i_assert(openssl_init_refcount > 0);
+
+	if (--openssl_init_refcount > 0)
+		return TRUE;
+
+	if (dovecot_openssl_engine != NULL) {
+		ENGINE_finish(dovecot_openssl_engine);
+		dovecot_openssl_engine = NULL;
+	}
+	/* OBJ_cleanup() is called automatically by EVP_cleanup() in
+	   newer versions. Doesn't hurt to call it anyway. */
+	OBJ_cleanup();
+#ifdef HAVE_SSL_COMP_FREE_COMPRESSION_METHODS
+	SSL_COMP_free_compression_methods();
+#endif
+	ENGINE_cleanup();
+	EVP_cleanup();
+	CRYPTO_cleanup_all_ex_data();
+#ifdef HAVE_OPENSSL_AUTO_THREAD_DEINIT
+	/* no cleanup needed */
+#elif defined(HAVE_OPENSSL_ERR_REMOVE_THREAD_STATE)
+	/* This was marked as deprecated in v1.1. */
+	ERR_remove_thread_state(NULL);
+#else
+	/* This was deprecated by ERR_remove_thread_state(NULL) in v1.0.0. */
+	ERR_remove_state(0);
+#endif
+	ERR_free_strings();
+#ifdef HAVE_OPENSSL_CLEANUP
+	OPENSSL_cleanup();
+#endif
+	return FALSE;
+}
+
+int dovecot_openssl_common_global_set_engine(const char *engine,
+					     const char **error_r)
+{
+	if (dovecot_openssl_engine != NULL)
+		return 1;
+
+	ENGINE_load_builtin_engines();
+	dovecot_openssl_engine = ENGINE_by_id(engine);
+	if (dovecot_openssl_engine == NULL) {
+		*error_r = t_strdup_printf("Unknown engine '%s'", engine);
+		return 0;
+	}
+	if (ENGINE_init(dovecot_openssl_engine) == 0) {
+		*error_r = t_strdup_printf("ENGINE_init(%s) failed", engine);
+		ENGINE_free(dovecot_openssl_engine);
+		dovecot_openssl_engine = NULL;
+		return -1;
+	}
+	if (ENGINE_set_default(dovecot_openssl_engine, ENGINE_METHOD_ALL) == 0) {
+		*error_r = t_strdup_printf("ENGINE_set_default(%s) failed", engine);
+		ENGINE_free(dovecot_openssl_engine);
+		dovecot_openssl_engine = NULL;
+		return -1;
+	}
+	return 1;
+}
diff --git a/src/lib-ssl-iostream/dovecot-openssl-common.h b/src/lib-ssl-iostream/dovecot-openssl-common.h
new file mode 100644
index 0000000..31854d3
--- /dev/null
+++ b/src/lib-ssl-iostream/dovecot-openssl-common.h
@@ -0,0 +1,16 @@
+#ifndef DOVECOT_OPENSSL_COMMON_H
+#define DOVECOT_OPENSSL_COMMON_H
+
+/* Initialize OpenSSL if this is the first instance.
+   Increase initialization reference count. */
+void dovecot_openssl_common_global_ref(void);
+/* Deinitialize OpenSSL if this is the last instance. Returns TRUE if there
+   are more instances left. */
+bool dovecot_openssl_common_global_unref(void);
+
+/* Set OpenSSL engine if it's not already set. Returns 1 on success, 0 if engine
+   is unknown, -1 on other error. error_r is set on 0/-1. */
+int dovecot_openssl_common_global_set_engine(const char *engine,
+					     const char **error_r);
+
+#endif
diff --git a/src/lib-ssl-iostream/iostream-openssl-common.c b/src/lib-ssl-iostream/iostream-openssl-common.c
new file mode 100644
index 0000000..04dc5ea
--- /dev/null
+++ b/src/lib-ssl-iostream/iostream-openssl-common.c
@@ -0,0 +1,343 @@
+/* Copyright (c) 2009-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "net.h"
+#include "str.h"
+#include "iostream-openssl.h"
+
+#include <openssl/x509v3.h>
+#include <openssl/err.h>
+#include <arpa/inet.h>
+
+/* openssl_min_protocol_to_options() scans this array for name and returns
+   version and opt. opt is used with SSL_set_options() and version is used with
+   SSL_set_min_proto_version(). Using either method should enable the same
+   SSL protocol versions. */
+static const struct {
+	const char *name;
+	int version;
+	long opt;
+} protocol_versions[] = {
+#ifdef TLS_ANY_VERSION
+	{ "ANY",	   TLS_ANY_VERSION,	0 },
+#else
+	{ "ANY",	   SSL3_VERSION,   0 },
+#endif
+	{ SSL_TXT_SSLV3,   SSL3_VERSION,   0 },
+	{ SSL_TXT_TLSV1,   TLS1_VERSION,   SSL_OP_NO_SSLv3 },
+	{ SSL_TXT_TLSV1_1, TLS1_1_VERSION, SSL_OP_NO_SSLv3 | SSL_OP_NO_TLSv1 },
+	{ SSL_TXT_TLSV1_2, TLS1_2_VERSION,
+		SSL_OP_NO_SSLv3 | SSL_OP_NO_TLSv1 | SSL_OP_NO_TLSv1_1 },
+#if defined(TLS1_3_VERSION)
+	{ "TLSv1.3",	   TLS1_3_VERSION,
+		SSL_OP_NO_SSLv3 | SSL_OP_NO_TLSv1 | SSL_OP_NO_TLSv1_1 |
+		SSL_OP_NO_TLSv1_2 },
+#endif
+	/* Use latest protocol version. If this is used on some
+	   ancient system which does not support ssl_min_protocol,
+	   ensure only TLSv1.2 is supported. */
+#ifdef TLS_MAX_VERSION
+	{ "LATEST",	   TLS_MAX_VERSION,
+#else
+	{ "LATEST",	   0,
+#endif
+		SSL_OP_NO_SSLv3 | SSL_OP_NO_TLSv1 | SSL_OP_NO_TLSv1_1 },
+};
+int openssl_min_protocol_to_options(const char *min_protocol, long *opt_r,
+				    int *version_r)
+{
+	unsigned i = 0;
+	for (; i < N_ELEMENTS(protocol_versions); i++) {
+		if (strcasecmp(protocol_versions[i].name, min_protocol) == 0)
+			break;
+	}
+	if (i >= N_ELEMENTS(protocol_versions))
+		return -1;
+
+	if (opt_r != NULL)
+		*opt_r = protocol_versions[i].opt;
+	if (version_r != NULL)
+		*version_r = protocol_versions[i].version;
+	return 0;
+}
+
+#if !defined(HAVE_X509_CHECK_HOST) || !defined(HAVE_X509_CHECK_IP_ASC)
+static const char *asn1_string_to_c(ASN1_STRING *asn_str)
+{
+	const char *cstr;
+	unsigned int len;
+
+	len = ASN1_STRING_length(asn_str);
+	cstr = t_strndup(ASN1_STRING_get0_data(asn_str), len);
+	if (strlen(cstr) != len) {
+		/* NULs in the name - could be some MITM attack.
+		   never allow. */
+		return "";
+	}
+	return cstr;
+}
+
+static const char *get_general_dns_name(const GENERAL_NAME *name)
+{
+	if (ASN1_STRING_type(name->d.ia5) != V_ASN1_IA5STRING)
+		return "";
+
+	return asn1_string_to_c(name->d.ia5);
+}
+
+static int get_general_ip_addr(const GENERAL_NAME *name, struct ip_addr *ip_r)
+{
+	if (ASN1_STRING_type(name->d.ip) != V_ASN1_OCTET_STRING)
+		return 0;
+	const unsigned char *data = ASN1_STRING_get0_data(name->d.ip);
+
+	if (name->d.ip->length == sizeof(ip_r->u.ip4.s_addr)) {
+		ip_r->family = AF_INET;
+		memcpy(&ip_r->u.ip4.s_addr, data, sizeof(ip_r->u.ip4.s_addr));
+	} else if (name->d.ip->length == sizeof(ip_r->u.ip6.s6_addr)) {
+		ip_r->family = AF_INET6;
+		memcpy(ip_r->u.ip6.s6_addr, data, sizeof(ip_r->u.ip6.s6_addr));
+	} else
+		return -1;
+	return 0;
+}
+
+static const char *get_cname(X509 *cert)
+{
+	X509_NAME *name;
+	X509_NAME_ENTRY *entry;
+	ASN1_STRING *str;
+	int cn_idx;
+
+	name = X509_get_subject_name(cert);
+	if (name == NULL)
+		return "";
+	cn_idx = X509_NAME_get_index_by_NID(name, NID_commonName, -1);
+	if (cn_idx == -1)
+		return "";
+	entry = X509_NAME_get_entry(name, cn_idx);
+	i_assert(entry != NULL);
+	str = X509_NAME_ENTRY_get_data(entry);
+	i_assert(str != NULL);
+	return asn1_string_to_c(str);
+}
+
+static bool openssl_hostname_equals(const char *ssl_name, const char *host)
+{
+	const char *p;
+
+	if (strcasecmp(ssl_name, host) == 0)
+		return TRUE;
+
+	/* check for *.example.com wildcard */
+	if (ssl_name[0] != '*' || ssl_name[1] != '.')
+		return FALSE;
+	p = strchr(host, '.');
+	return p != NULL && strcasecmp(ssl_name+2, p+1) == 0;
+}
+#endif
+
+bool openssl_cert_match_name(SSL *ssl, const char *verify_name,
+			     const char **reason_r)
+{
+	X509 *cert;
+	bool ret;
+
+	*reason_r = NULL;
+
+	cert = SSL_get_peer_certificate(ssl);
+	i_assert(cert != NULL);
+
+#if defined(HAVE_X509_CHECK_HOST) && defined(HAVE_X509_CHECK_IP_ASC)
+	char *peername;
+	int check_res;
+
+	/* First check DNS name agains CommonName or SubjectAltNames.
+	   If failed, check IP addresses. */
+	if ((check_res = X509_check_host(cert, verify_name, strlen(verify_name),
+					 X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS,
+					 &peername)) == 1) {
+		*reason_r = t_strdup_printf("Matched to %s", peername);
+		free(peername);
+		ret = TRUE;
+	} else if (check_res == 0 &&
+		   (check_res = X509_check_ip_asc(cert, verify_name, 0)) == 1) {
+		*reason_r = t_strdup_printf("Matched to IP address %s", verify_name);
+		ret = TRUE;
+	} else if (check_res == 0) {
+		*reason_r = "did not match to any IP or DNS fields";
+		ret = FALSE;
+	} else {
+		*reason_r = "Malformed input";
+		ret = FALSE;
+	}
+#else
+	STACK_OF(GENERAL_NAME) *gnames;
+	const GENERAL_NAME *gn;
+	struct ip_addr ip;
+	const char *dnsname;
+	bool dns_names = FALSE;
+	unsigned int i, count;
+
+	/* verify against SubjectAltNames */
+	gnames = X509_get_ext_d2i(cert, NID_subject_alt_name, NULL, NULL);
+	count = gnames == NULL ? 0 : sk_GENERAL_NAME_num(gnames);
+
+	i_zero(&ip);
+	/* try to convert verify_name to IP */
+	if (inet_pton(AF_INET6, verify_name, &ip.u.ip6) == 1)
+		ip.family = AF_INET6;
+	else if (inet_pton(AF_INET, verify_name, &ip.u.ip4) == 1)
+		ip.family = AF_INET;
+	else
+		i_zero(&ip);
+
+	for (i = 0; i < count; i++) {
+		gn = sk_GENERAL_NAME_value(gnames, i);
+
+		if (gn->type == GEN_DNS) {
+			dns_names = TRUE;
+			dnsname = get_general_dns_name(gn);
+			if (openssl_hostname_equals(dnsname, verify_name)) {
+				*reason_r = t_strdup_printf(
+					"Matches DNS name in SubjectAltNames: %s", dnsname);
+				break;
+			}
+		} else if (gn->type == GEN_IPADD) {
+			struct ip_addr ip_2;
+			i_zero(&ip_2);
+			dns_names = TRUE;
+			if (get_general_ip_addr(gn, &ip_2) == 0 &&
+			    net_ip_compare(&ip, &ip_2)) {
+				*reason_r = t_strdup_printf(
+					"Matches IP in SubjectAltNames: %s", net_ip2addr(&ip_2));
+				break;
+			}
+		}
+	}
+	sk_GENERAL_NAME_pop_free(gnames, GENERAL_NAME_free);
+
+	/* verify against CommonName only when there wasn't any DNS
+	   SubjectAltNames */
+	if (dns_names) {
+		i_assert(*reason_r != NULL || i == count);
+		if (i == count) {
+			*reason_r = t_strdup_printf(
+				"No match to %u SubjectAltNames",
+				count);
+			ret = FALSE;
+		} else {
+			ret = TRUE;
+		}
+	} else {
+		const char *cname = get_cname(cert);
+
+		if (openssl_hostname_equals(cname, verify_name)) {
+			ret = TRUE;
+			*reason_r = t_strdup_printf(
+				"Matches to CommonName: %s", cname);
+		} else {
+			*reason_r = t_strdup_printf(
+				"No match to CommonName=%s or %u SubjectAltNames",
+				cname, count);
+			ret = FALSE;
+		}
+	}
+#endif
+	X509_free(cert);
+	return ret;
+}
+
+static const char *ssl_err2str(unsigned long err, const char *data, int flags)
+{
+	const char *ret;
+	char *buf;
+	size_t err_size = 256;
+
+	buf = t_malloc0(err_size);
+	ERR_error_string_n(err, buf, err_size-1);
+	ret = buf;
+
+	if ((flags & ERR_TXT_STRING) != 0)
+		ret = t_strdup_printf("%s: %s", buf, data);
+	return ret;
+}
+
+const char *openssl_iostream_error(void)
+{
+	string_t *errstr = NULL;
+	unsigned long err;
+	const char *data, *final_error;
+	int flags;
+
+	while ((err = ERR_get_error_line_data(NULL, NULL, &data, &flags)) != 0) {
+		if (ERR_GET_REASON(err) == ERR_R_MALLOC_FAILURE)
+			i_fatal_status(FATAL_OUTOFMEM, "OpenSSL malloc() failed");
+		if (ERR_peek_error() == 0)
+			break;
+		if (errstr == NULL)
+			errstr = t_str_new(128);
+		else
+			str_append(errstr, ", ");
+		str_append(errstr, ssl_err2str(err, data, flags));
+	}
+	if (err == 0) {
+		if (errno != 0)
+			final_error = strerror(errno);
+		else
+			final_error = "Unknown error";
+	} else {
+		final_error = ssl_err2str(err, data, flags);
+	}
+	if (errstr == NULL)
+		return final_error;
+	else {
+		str_printfa(errstr, ", %s", final_error);
+		return str_c(errstr);
+	}
+}
+
+const char *openssl_iostream_key_load_error(void)
+{
+       unsigned long err = ERR_peek_error();
+
+       if (ERR_GET_LIB(err) == ERR_LIB_X509 &&
+           ERR_GET_REASON(err) == X509_R_KEY_VALUES_MISMATCH)
+               return "Key is for a different cert than ssl_cert";
+       else
+               return openssl_iostream_error();
+}
+
+static bool is_pem_key(const char *cert)
+{
+	return strstr(cert, "PRIVATE KEY---") != NULL;
+}
+
+const char *
+openssl_iostream_use_certificate_error(const char *cert, const char *set_name)
+{
+	unsigned long err;
+
+	if (cert[0] == '\0')
+		return "The certificate is empty";
+
+	err = ERR_peek_error();
+	if (ERR_GET_LIB(err) != ERR_LIB_PEM ||
+	    ERR_GET_REASON(err) != PEM_R_NO_START_LINE)
+		return openssl_iostream_error();
+	else if (is_pem_key(cert)) {
+		return "The file contains a private key "
+			"(you've mixed ssl_cert and ssl_key settings)";
+	} else if (set_name != NULL && strchr(cert, '\n') == NULL) {
+		return t_strdup_printf("There is no valid PEM certificate. "
+			"(You probably forgot '<' from %s=<%s)", set_name, cert);
+	} else {
+		return "There is no valid PEM certificate.";
+	}
+}
+
+void openssl_iostream_clear_errors(void)
+{
+	while (ERR_get_error() != 0)
+		;
+}
diff --git a/src/lib-ssl-iostream/iostream-openssl-context.c b/src/lib-ssl-iostream/iostream-openssl-context.c
new file mode 100644
index 0000000..fe9b059
--- /dev/null
+++ b/src/lib-ssl-iostream/iostream-openssl-context.c
@@ -0,0 +1,755 @@
+/* Copyright (c) 2009-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "safe-memset.h"
+#include "iostream-openssl.h"
+#include "dovecot-openssl-common.h"
+
+#include <openssl/crypto.h>
+#include <openssl/rsa.h>
+#include <openssl/dh.h>
+#include <openssl/bn.h>
+#include <openssl/x509.h>
+#include <openssl/pem.h>
+#include <openssl/ssl.h>
+#include <openssl/err.h>
+
+#if !defined(OPENSSL_NO_ECDH) && OPENSSL_VERSION_NUMBER >= 0x10000000L
+#  define HAVE_ECDH
+#endif
+
+struct ssl_iostream_password_context {
+	const char *password;
+	const char *error;
+};
+
+static bool ssl_global_initialized = FALSE;
+int dovecot_ssl_extdata_index;
+
+static RSA *ssl_gen_rsa_key(SSL *ssl ATTR_UNUSED,
+			    int is_export ATTR_UNUSED, int keylength)
+{
+#ifdef HAVE_RSA_GENERATE_KEY_EX
+	BIGNUM *bn = BN_new();
+	RSA *rsa = RSA_new();
+
+	if (bn != NULL && BN_set_word(bn, RSA_F4) != 0 &&
+	    RSA_generate_key_ex(rsa, keylength, bn, NULL) != 0) {
+		BN_free(bn);
+		return rsa;
+	}
+
+	if (bn != NULL)
+		BN_free(bn);
+	if (rsa != NULL)
+		RSA_free(rsa);
+	return NULL;
+#else
+	return RSA_generate_key(keylength, RSA_F4, NULL, NULL);
+#endif
+}
+
+static DH *ssl_tmp_dh_callback(SSL *ssl ATTR_UNUSED,
+			       int is_export ATTR_UNUSED, int keylength ATTR_UNUSED)
+{
+	i_error("Diffie-Hellman key exchange requested, "
+		"but no DH parameters provided. Set ssl_dh=</path/to/dh.pem");
+	return NULL;
+}
+
+static int
+pem_password_callback(char *buf, int size, int rwflag ATTR_UNUSED,
+		      void *userdata)
+{
+	struct ssl_iostream_password_context *ctx = userdata;
+
+	if (ctx->password == NULL) {
+		ctx->error = "SSL private key file is password protected, "
+			"but password isn't given";
+		return 0;
+	}
+
+	if (i_strocpy(buf, ctx->password, size) < 0) {
+		ctx->error = "SSL private key password is too long";
+		return 0;
+	}
+	return strlen(buf);
+}
+
+int openssl_iostream_load_key(const struct ssl_iostream_cert *set,
+			      const char *set_name,
+			      EVP_PKEY **pkey_r, const char **error_r)
+{
+	struct ssl_iostream_password_context ctx;
+	EVP_PKEY *pkey;
+	BIO *bio;
+	char *key;
+
+	key = t_strdup_noconst(set->key);
+	bio = BIO_new_mem_buf(key, strlen(key));
+	if (bio == NULL) {
+		*error_r = t_strdup_printf("BIO_new_mem_buf() failed: %s",
+					   openssl_iostream_error());
+		safe_memset(key, 0, strlen(key));
+		return -1;
+	}
+
+	ctx.password = set->key_password;
+	ctx.error = NULL;
+
+	pkey = PEM_read_bio_PrivateKey(bio, NULL, pem_password_callback, &ctx);
+	if (pkey == NULL && ctx.error == NULL) {
+		ctx.error = t_strdup_printf(
+			"Couldn't parse private SSL key (%s setting)%s: %s",
+			set_name,
+			ctx.password != NULL ?
+				" (maybe ssl_key_password is wrong?)" :
+				"",
+			openssl_iostream_error());
+	}
+	BIO_free(bio);
+
+	safe_memset(key, 0, strlen(key));
+	*pkey_r = pkey;
+	*error_r = ctx.error;
+	return pkey == NULL ? -1 : 0;
+}
+
+static
+int openssl_iostream_load_dh(const struct ssl_iostream_settings *set,
+			     DH **dh_r, const char **error_r)
+{
+	DH *dh;
+	BIO *bio;
+	char *dhvalue;
+
+	dhvalue = t_strdup_noconst(set->dh);
+	bio = BIO_new_mem_buf(dhvalue, strlen(dhvalue));
+
+	if (bio == NULL) {
+		*error_r = t_strdup_printf("BIO_new_mem_buf() failed: %s",
+					   openssl_iostream_error());
+		return -1;
+	}
+
+	dh = NULL;
+	dh = PEM_read_bio_DHparams(bio, &dh, NULL, NULL);
+
+	if (dh == NULL) {
+		*error_r = t_strdup_printf("Couldn't parse DH parameters: %s",
+					   openssl_iostream_error());
+	}
+	BIO_free(bio);
+	*dh_r = dh;
+	return dh == NULL ? -1 : 0;
+}
+
+static int
+ssl_iostream_ctx_use_key(struct ssl_iostream_context *ctx, const char *set_name,
+			 const struct ssl_iostream_cert *set,
+			 const char **error_r)
+{
+	EVP_PKEY *pkey;
+	int ret = 0;
+
+	if (openssl_iostream_load_key(set, set_name, &pkey, error_r) < 0)
+		return -1;
+	if (SSL_CTX_use_PrivateKey(ctx->ssl_ctx, pkey) == 0) {
+		*error_r = t_strdup_printf(
+			"Can't load SSL private key (%s setting): %s",
+			set_name, openssl_iostream_key_load_error());
+		ret = -1;
+	}
+	EVP_PKEY_free(pkey);
+	return ret;
+}
+
+static int
+ssl_iostream_ctx_use_dh(struct ssl_iostream_context *ctx,
+			const struct ssl_iostream_settings *set,
+			const char **error_r)
+{
+	DH *dh;
+	int ret = 0;
+	if (*set->dh == '\0') {
+		return 0;
+	}
+	if (openssl_iostream_load_dh(set, &dh, error_r) < 0)
+		return -1;
+	if (SSL_CTX_set_tmp_dh(ctx->ssl_ctx, dh) == 0) {
+		 *error_r = t_strdup_printf(
+			"Can't load DH parameters (ssl_dh setting): %s",
+			openssl_iostream_key_load_error());
+		ret = -1;
+	}
+	DH_free(dh);
+	return ret;
+}
+
+static int ssl_ctx_use_certificate_chain(SSL_CTX *ctx, const char *cert)
+{
+	/* mostly just copy&pasted from SSL_CTX_use_certificate_chain_file() */
+	BIO *in;
+	X509 *x;
+	int ret = 0;
+
+	in = BIO_new_mem_buf(t_strdup_noconst(cert), strlen(cert));
+	if (in == NULL)
+		i_fatal("BIO_new_mem_buf() failed");
+
+	x = PEM_read_bio_X509(in, NULL, NULL, NULL);
+	if (x == NULL)
+		goto end;
+
+	ret = SSL_CTX_use_certificate(ctx, x);
+	if (ERR_peek_error() != 0)
+		ret = 0;
+
+	if (ret != 0) {
+#ifdef HAVE_SSL_CTX_SET_CURRENT_CERT
+		SSL_CTX_select_current_cert(ctx, x);
+#endif
+		/* If we could set up our certificate, now proceed to
+		 * the CA certificates.
+		 */
+		X509 *ca;
+		int r;
+		unsigned long err;
+		
+		while ((ca = PEM_read_bio_X509(in,NULL,NULL,NULL)) != NULL) {
+#ifdef HAVE_SSL_CTX_ADD0_CHAIN_CERT
+			r = SSL_CTX_add0_chain_cert(ctx, ca);
+#else
+			r = SSL_CTX_add_extra_chain_cert(ctx, ca);
+#endif
+			if (r == 0) {
+				X509_free(ca);
+				ret = 0;
+				goto end;
+			}
+		}
+		/* When the while loop ends, it's usually just EOF. */
+		err = ERR_peek_last_error();
+		if (ERR_GET_LIB(err) == ERR_LIB_PEM && ERR_GET_REASON(err) == PEM_R_NO_START_LINE)
+			ERR_clear_error();
+		else 
+			ret = 0; /* some real error */
+		}
+
+end:
+	if (x != NULL) X509_free(x);
+	BIO_free(in);
+#ifdef HAVE_SSL_CTX_SET_CURRENT_CERT
+	SSL_CTX_set_current_cert(ctx, SSL_CERT_SET_FIRST);
+#endif
+	return ret;
+}
+
+static int load_ca(X509_STORE *store, const char *ca,
+		   STACK_OF(X509_NAME) **xnames_r)
+{
+	/* mostly just copy&pasted from X509_load_cert_crl_file() */
+	STACK_OF(X509_INFO) *inf;
+	STACK_OF(X509_NAME) *xnames;
+	X509_INFO *itmp;
+	X509_NAME *xname;
+	BIO *bio;
+	int i;
+
+	bio = BIO_new_mem_buf(t_strdup_noconst(ca), strlen(ca));
+	if (bio == NULL)
+		i_fatal("BIO_new_mem_buf() failed");
+	inf = PEM_X509_INFO_read_bio(bio, NULL, NULL, NULL);
+	BIO_free(bio);
+
+	if (inf == NULL)
+		return -1;
+
+	xnames = sk_X509_NAME_new_null();
+	if (xnames == NULL)
+		i_fatal("sk_X509_NAME_new_null() failed");
+	for(i = 0; i < sk_X509_INFO_num(inf); i++) {
+		itmp = sk_X509_INFO_value(inf, i);
+		if(itmp->x509 != NULL) {
+			X509_STORE_add_cert(store, itmp->x509);
+			xname = X509_get_subject_name(itmp->x509);
+			if (xname != NULL)
+				xname = X509_NAME_dup(xname);
+			if (xname != NULL)
+				sk_X509_NAME_push(xnames, xname);
+		}
+		if(itmp->crl != NULL)
+			X509_STORE_add_crl(store, itmp->crl);
+	}
+	sk_X509_INFO_pop_free(inf, X509_INFO_free);
+	*xnames_r = xnames;
+	return 0;
+}
+
+static int
+load_ca_locations(struct ssl_iostream_context *ctx, const char *ca_file,
+		  const char *ca_dir, const char **error_r)
+{
+	if (SSL_CTX_load_verify_locations(ctx->ssl_ctx, ca_file, ca_dir) != 0)
+		return 0;
+
+	if (ca_dir == NULL) {
+		*error_r = t_strdup_printf(
+			"Can't load CA certs from %s "
+			"(ssl_client_ca_file setting): %s",
+			ca_file, openssl_iostream_error());
+	} else if (ca_file == NULL) {
+		*error_r = t_strdup_printf(
+			"Can't load CA certs from directory %s "
+			"(ssl_client_ca_dir setting): %s",
+			ca_dir, openssl_iostream_error());
+	} else {
+		*error_r = t_strdup_printf(
+			"Can't load CA certs from file %s and directory %s "
+			"(ssl_client_ca_* settings): %s",
+			ca_file, ca_dir, openssl_iostream_error());
+	}
+	return -1;
+}
+
+static void
+ssl_iostream_ctx_verify_remote_cert(struct ssl_iostream_context *ctx,
+				    STACK_OF(X509_NAME) *ca_names)
+{
+#if OPENSSL_VERSION_NUMBER >= 0x00907000L
+	if (!ctx->set.skip_crl_check) {
+		X509_STORE *store;
+
+		store = SSL_CTX_get_cert_store(ctx->ssl_ctx);
+		X509_STORE_set_flags(store, X509_V_FLAG_CRL_CHECK |
+				     X509_V_FLAG_CRL_CHECK_ALL);
+	}
+#endif
+
+	SSL_CTX_set_client_CA_list(ctx->ssl_ctx, ca_names);
+}
+
+#ifdef HAVE_SSL_GET_SERVERNAME
+static int ssl_servername_callback(SSL *ssl, int *al ATTR_UNUSED,
+				   void *context ATTR_UNUSED)
+{
+	struct ssl_iostream *ssl_io;
+	const char *host, *error;
+
+	ssl_io = SSL_get_ex_data(ssl, dovecot_ssl_extdata_index);
+	host = SSL_get_servername(ssl, TLSEXT_NAMETYPE_host_name);
+	if (SSL_get_servername_type(ssl) != -1) {
+		i_free(ssl_io->sni_host);
+		ssl_io->sni_host = i_strdup(host);
+	} else if (ssl_io->verbose) {
+		i_debug("SSL_get_servername() failed");
+	}
+
+	if (ssl_io->sni_callback != NULL) {
+		if (ssl_io->sni_callback(ssl_io->sni_host, &error,
+					 ssl_io->sni_context) < 0) {
+			openssl_iostream_set_error(ssl_io, error);
+			return SSL_TLSEXT_ERR_ALERT_FATAL;
+		}
+	}
+	return SSL_TLSEXT_ERR_OK;
+}
+#endif
+
+static int
+ssl_iostream_context_load_ca(struct ssl_iostream_context *ctx,
+			     const struct ssl_iostream_settings *set,
+			     const char **error_r)
+{
+	X509_STORE *store;
+	STACK_OF(X509_NAME) *xnames = NULL;
+	const char *ca_file, *ca_dir;
+	bool have_ca = FALSE;
+
+	if (set->ca != NULL) {
+		store = SSL_CTX_get_cert_store(ctx->ssl_ctx);
+		if (load_ca(store, set->ca, &xnames) < 0) {
+			*error_r = t_strdup_printf("Couldn't parse ssl_ca: %s",
+						   openssl_iostream_error());
+			return -1;
+		}
+		ssl_iostream_ctx_verify_remote_cert(ctx, xnames);
+		have_ca = TRUE;
+	}
+	ca_file = set->ca_file == NULL || *set->ca_file == '\0' ?
+		NULL : set->ca_file;
+	ca_dir = set->ca_dir == NULL || *set->ca_dir == '\0' ?
+		NULL : set->ca_dir;
+	if (ca_file != NULL || ca_dir != NULL) {
+		if (load_ca_locations(ctx, ca_file, ca_dir, error_r) < 0)
+			return -1;
+		have_ca = TRUE;
+	}
+	if (!have_ca && ctx->client_ctx) {
+		if (SSL_CTX_set_default_verify_paths(ctx->ssl_ctx) != 1) {
+			*error_r = t_strdup_printf(
+				"Can't load default CA locations: %s (ssl_client_ca_* settings missing)",
+				openssl_iostream_error());
+			return -1;
+		}
+	} else if (!have_ca) {
+		*error_r = "Can't verify remote client certs without CA (ssl_ca setting)";
+		return -1;
+	}
+	return 0;
+}
+
+static int
+ssl_iostream_context_set(struct ssl_iostream_context *ctx,
+			 const struct ssl_iostream_settings *set,
+			 const char **error_r)
+{
+	ssl_iostream_settings_init_from(ctx->pool, &ctx->set, set);
+	if (set->cipher_list != NULL &&
+	    SSL_CTX_set_cipher_list(ctx->ssl_ctx, set->cipher_list) == 0) {
+		*error_r = t_strdup_printf(
+			"Can't set cipher list to '%s' (ssl_cipher_list setting): %s",
+			set->cipher_list, openssl_iostream_error());
+		return -1;
+	}
+#ifdef HAVE_SSL_CTX_SET1_CURVES_LIST
+	if (set->curve_list != NULL && strlen(set->curve_list) > 0 &&
+		SSL_CTX_set1_curves_list(ctx->ssl_ctx, set->curve_list) == 0) {
+		*error_r = t_strdup_printf(
+			"Can't set curve list to '%s' (ssl_curve_list setting)",
+			set->curve_list);
+		return -1;
+	}
+#endif
+#ifdef HAVE_SSL_CTX_SET_CIPHERSUITES
+	if (set->ciphersuites != NULL &&
+	    SSL_CTX_set_ciphersuites(ctx->ssl_ctx, set->ciphersuites) == 0) {
+		*error_r = t_strdup_printf("Can't set ciphersuites to '%s': %s",
+			set->ciphersuites, openssl_iostream_error());
+		return -1;
+	}
+#endif
+	if (set->prefer_server_ciphers) {
+		SSL_CTX_set_options(ctx->ssl_ctx,
+				    SSL_OP_CIPHER_SERVER_PREFERENCE);
+	}
+	if (ctx->set.min_protocol != NULL) {
+		long opts;
+		int min_protocol;
+		if (openssl_min_protocol_to_options(ctx->set.min_protocol,
+						    &opts, &min_protocol) < 0) {
+			*error_r = t_strdup_printf(
+					"Unknown ssl_min_protocol setting '%s'",
+					set->min_protocol);
+			return -1;
+		}
+#ifdef HAVE_SSL_CTX_SET_MIN_PROTO_VERSION
+		SSL_CTX_set_min_proto_version(ctx->ssl_ctx, min_protocol);
+#else
+		SSL_CTX_set_options(ctx->ssl_ctx, opts);
+#endif
+	}
+
+	if (set->cert.cert != NULL &&
+	    ssl_ctx_use_certificate_chain(ctx->ssl_ctx, set->cert.cert) == 0) {
+		*error_r = t_strdup_printf(
+			"Can't load SSL certificate (ssl_cert setting): %s",
+			openssl_iostream_use_certificate_error(set->cert.cert, NULL));
+		return -1;
+	}
+	if (set->cert.key != NULL) {
+		if (ssl_iostream_ctx_use_key(ctx, "ssl_key", &set->cert, error_r) < 0)
+			return -1;
+	}
+	if (set->alt_cert.cert != NULL &&
+	    ssl_ctx_use_certificate_chain(ctx->ssl_ctx, set->alt_cert.cert) == 0) {
+		*error_r = t_strdup_printf(
+			"Can't load alternative SSL certificate "
+			"(ssl_alt_cert setting): %s",
+			openssl_iostream_use_certificate_error(set->alt_cert.cert, NULL));
+		return -1;
+	}
+	if (set->alt_cert.key != NULL) {
+		if (ssl_iostream_ctx_use_key(ctx, "ssl_alt_key", &set->alt_cert, error_r) < 0)
+			return -1;
+	}
+
+	if (set->dh != NULL) {
+		if (ssl_iostream_ctx_use_dh(ctx, set, error_r) < 0)
+			return -1;
+	}
+
+	/* set trusted CA certs */
+	if (set->verify_remote_cert) {
+		if (ssl_iostream_context_load_ca(ctx, set, error_r) < 0)
+			return -1;
+	}
+
+	if (set->cert_username_field != NULL) {
+		ctx->username_nid = OBJ_txt2nid(set->cert_username_field);
+		if (ctx->username_nid == NID_undef) {
+			*error_r = t_strdup_printf(
+				"Invalid cert_username_field: %s",
+				set->cert_username_field);
+			return -1;
+		}
+	}
+#ifdef HAVE_SSL_GET_SERVERNAME
+	if (!ctx->client_ctx) {
+		if (SSL_CTX_set_tlsext_servername_callback(ctx->ssl_ctx,
+					ssl_servername_callback) != 1) {
+			if (set->verbose)
+				i_debug("OpenSSL library doesn't support SNI");
+		}
+	}
+#endif
+	return 0;
+}
+
+#if defined(HAVE_ECDH) && !defined(SSL_CTX_set_ecdh_auto)
+static int
+ssl_proxy_ctx_get_pkey_ec_curve_name(const struct ssl_iostream_settings *set,
+				     int *nid_r, const char **error_r)
+{
+	int nid = 0;
+	EVP_PKEY *pkey;
+	EC_KEY *eckey;
+	const EC_GROUP *ecgrp;
+
+	if (set->cert.key != NULL) {
+		if (openssl_iostream_load_key(&set->cert, "ssl_key", &pkey, error_r) < 0)
+			return -1;
+
+		if ((eckey = EVP_PKEY_get1_EC_KEY(pkey)) != NULL &&
+		    (ecgrp = EC_KEY_get0_group(eckey)) != NULL)
+			nid = EC_GROUP_get_curve_name(ecgrp);
+		else {
+			/* clear errors added by the above calls */
+			openssl_iostream_clear_errors();
+		}
+		EVP_PKEY_free(pkey);
+	}
+	if (nid == 0 && set->alt_cert.key != NULL) {
+		if (openssl_iostream_load_key(&set->alt_cert, "ssl_alt_key", &pkey, error_r) < 0)
+			return -1;
+
+		if ((eckey = EVP_PKEY_get1_EC_KEY(pkey)) != NULL &&
+		    (ecgrp = EC_KEY_get0_group(eckey)) != NULL)
+			nid = EC_GROUP_get_curve_name(ecgrp);
+		else {
+			/* clear errors added by the above calls */
+			openssl_iostream_clear_errors();
+		}
+		EVP_PKEY_free(pkey);
+	}
+
+	*nid_r = nid;
+	return 0;
+}
+#endif
+
+static int
+ssl_proxy_ctx_set_crypto_params(SSL_CTX *ssl_ctx,
+				const struct ssl_iostream_settings *set,
+				const char **error_r ATTR_UNUSED)
+{
+#if defined(HAVE_ECDH) && !defined(SSL_CTX_set_ecdh_auto)
+	EC_KEY *ecdh;
+	int nid;
+	const char *curve_name;
+#endif
+	if (SSL_CTX_need_tmp_RSA(ssl_ctx) != 0)
+		SSL_CTX_set_tmp_rsa_callback(ssl_ctx, ssl_gen_rsa_key);
+	if (set->dh == NULL || *set->dh == '\0')
+		SSL_CTX_set_tmp_dh_callback(ssl_ctx, ssl_tmp_dh_callback);
+#ifdef HAVE_ECDH
+	/* In the non-recommended situation where ECDH cipher suites are being
+	   used instead of ECDHE, do not reuse the same ECDH key pair for
+	   different sessions. This option improves forward secrecy. */
+	SSL_CTX_set_options(ssl_ctx, SSL_OP_SINGLE_ECDH_USE);
+#ifdef SSL_CTX_set_ecdh_auto
+	/* OpenSSL >= 1.0.2 automatically handles ECDH temporary key parameter
+	   selection. The return value of this function changes is changed to
+	   bool in OpenSSL 1.1 and is int in OpenSSL 1.0.2+ */
+	if ((long)(SSL_CTX_set_ecdh_auto(ssl_ctx, 1)) == 0) {
+		/* shouldn't happen */
+		*error_r = t_strdup_printf("SSL_CTX_set_ecdh_auto() failed: %s",
+					   openssl_iostream_error());
+		return -1;
+	}
+#else
+	/* For OpenSSL < 1.0.2, ECDH temporary key parameter selection must be
+	   performed manually. Attempt to select the same curve as that used
+	   in the server's private EC key file. Otherwise fall back to the
+	   NIST P-384 (secp384r1) curve to be compliant with RFC 6460 when
+	   AES-256 TLS cipher suites are in use. This fall back option does
+	   however make Dovecot non-compliant with RFC 6460 which requires
+	   curve NIST P-256 (prime256v1) be used when AES-128 TLS cipher
+	   suites are in use. At least the non-compliance is in the form of
+	   providing too much security rather than too little. */
+	if (ssl_proxy_ctx_get_pkey_ec_curve_name(set, &nid, error_r) < 0)
+		return -1;
+	ecdh = EC_KEY_new_by_curve_name(nid);
+	if (ecdh == NULL) {
+		/* Fall back option */
+		nid = NID_secp384r1;
+		ecdh = EC_KEY_new_by_curve_name(nid);
+	}
+	if ((curve_name = OBJ_nid2sn(nid)) != NULL && set->verbose) {
+		i_debug("SSL: elliptic curve %s will be used for ECDH and"
+			" ECDHE key exchanges", curve_name);
+	}
+	if (ecdh != NULL) {
+		SSL_CTX_set_tmp_ecdh(ssl_ctx, ecdh);
+		EC_KEY_free(ecdh);
+	}
+#endif
+#endif
+#ifdef SSL_OP_SINGLE_DH_USE
+	/* Improves forward secrecy with DH parameters, especially if the
+	   parameters used aren't strong primes. See OpenSSL manual. */
+	SSL_CTX_set_options(ssl_ctx, SSL_OP_SINGLE_DH_USE);
+#endif
+	return 0;
+}
+
+static int
+ssl_iostream_context_init_common(struct ssl_iostream_context *ctx,
+				 const struct ssl_iostream_settings *set,
+				 const char **error_r)
+{
+	unsigned long ssl_ops = SSL_OP_NO_SSLv2 |
+		(SSL_OP_ALL & ~SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS);
+
+	ctx->pool = pool_alloconly_create("ssl iostream context", 4096);
+
+	/* enable all SSL workarounds, except empty fragments as it
+	   makes SSL more vulnerable against attacks */
+#ifdef SSL_OP_NO_COMPRESSION
+	if (!set->compression)
+		ssl_ops |= SSL_OP_NO_COMPRESSION;
+#endif
+#ifdef SSL_OP_NO_TICKET
+	if (!set->tickets)
+		ssl_ops |= SSL_OP_NO_TICKET;
+#endif
+	SSL_CTX_set_options(ctx->ssl_ctx, ssl_ops);
+#ifdef SSL_MODE_RELEASE_BUFFERS
+	SSL_CTX_set_mode(ctx->ssl_ctx, SSL_MODE_RELEASE_BUFFERS);
+#endif
+#ifdef SSL_MODE_ENABLE_PARTIAL_WRITE
+	SSL_CTX_set_mode(ctx->ssl_ctx, SSL_MODE_ENABLE_PARTIAL_WRITE);
+#endif
+#ifdef SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER
+	SSL_CTX_set_mode(ctx->ssl_ctx, SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER);
+#endif
+	if (ssl_proxy_ctx_set_crypto_params(ctx->ssl_ctx, set, error_r) < 0)
+		return -1;
+
+	return ssl_iostream_context_set(ctx, set, error_r);
+}
+
+int openssl_iostream_context_init_client(const struct ssl_iostream_settings *set,
+					 struct ssl_iostream_context **ctx_r,
+					 const char **error_r)
+{
+	struct ssl_iostream_context *ctx;
+	SSL_CTX *ssl_ctx;
+
+	if ((ssl_ctx = SSL_CTX_new(SSLv23_client_method())) == NULL) {
+		*error_r = t_strdup_printf("SSL_CTX_new() failed: %s",
+					   openssl_iostream_error());
+		return -1;
+	}
+	SSL_CTX_set_mode(ssl_ctx, SSL_MODE_ENABLE_PARTIAL_WRITE);
+
+	ctx = i_new(struct ssl_iostream_context, 1);
+	ctx->refcount = 1;
+	ctx->ssl_ctx = ssl_ctx;
+	ctx->client_ctx = TRUE;
+	if (ssl_iostream_context_init_common(ctx, set, error_r) < 0) {
+		ssl_iostream_context_unref(&ctx);
+		return -1;
+	}
+	*ctx_r = ctx;
+	return 0;
+}
+
+int openssl_iostream_context_init_server(const struct ssl_iostream_settings *set,
+					 struct ssl_iostream_context **ctx_r,
+					 const char **error_r)
+{
+	struct ssl_iostream_context *ctx;
+	SSL_CTX *ssl_ctx;
+
+	if ((ssl_ctx = SSL_CTX_new(SSLv23_server_method())) == NULL) {
+		*error_r = t_strdup_printf("SSL_CTX_new() failed: %s",
+					   openssl_iostream_error());
+		return -1;
+	}
+
+	ctx = i_new(struct ssl_iostream_context, 1);
+	ctx->refcount = 1;
+	ctx->ssl_ctx = ssl_ctx;
+	if (ssl_iostream_context_init_common(ctx, set, error_r) < 0) {
+		ssl_iostream_context_unref(&ctx);
+		return -1;
+	}
+	*ctx_r = ctx;
+	return 0;
+}
+
+void openssl_iostream_context_ref(struct ssl_iostream_context *ctx)
+{
+	i_assert(ctx->refcount > 0);
+	ctx->refcount++;
+}
+
+void openssl_iostream_context_unref(struct ssl_iostream_context *ctx)
+{
+	i_assert(ctx->refcount > 0);
+	if (--ctx->refcount > 0)
+		return;
+
+	SSL_CTX_free(ctx->ssl_ctx);
+	pool_unref(&ctx->pool);
+	i_free(ctx);
+}
+
+void openssl_iostream_global_deinit(void)
+{
+	if (!ssl_global_initialized)
+		return;
+	dovecot_openssl_common_global_unref();
+}
+
+int openssl_iostream_global_init(const struct ssl_iostream_settings *set,
+				 const char **error_r)
+{
+	static char dovecot[] = "dovecot";
+	const char *error;
+
+	if (ssl_global_initialized)
+		return 0;
+
+	ssl_global_initialized = TRUE;
+	dovecot_openssl_common_global_ref();
+
+	dovecot_ssl_extdata_index =
+		SSL_get_ex_new_index(0, dovecot, NULL, NULL, NULL);
+
+	if (set->crypto_device != NULL && *set->crypto_device != '\0') {
+		switch (dovecot_openssl_common_global_set_engine(set->crypto_device, &error)) {
+		case 0:
+			error = t_strdup_printf(
+				"Unknown ssl_crypto_device: %s",
+				set->crypto_device);
+			/* fall through */
+		case -1:
+			*error_r = error;
+			/* we'll deinit at exit in any case */
+			return -1;
+		}
+	}
+	return 0;
+}
diff --git a/src/lib-ssl-iostream/iostream-openssl.c b/src/lib-ssl-iostream/iostream-openssl.c
new file mode 100644
index 0000000..6920c53
--- /dev/null
+++ b/src/lib-ssl-iostream/iostream-openssl.c
@@ -0,0 +1,946 @@
+/* Copyright (c) 2009-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "istream-private.h"
+#include "ostream-private.h"
+#include "iostream-openssl.h"
+
+#include <openssl/rand.h>
+#include <openssl/err.h>
+
+static void openssl_iostream_free(struct ssl_iostream *ssl_io);
+
+void openssl_iostream_set_error(struct ssl_iostream *ssl_io, const char *str)
+{
+	char *new_str;
+
+	/* i_debug() may sometimes be overriden, making it write to this very
+	   same SSL stream, in which case the provided str may be invalidated
+	   before it is even used. Therefore, we duplicate it immediately. */
+	new_str = i_strdup(str);
+
+	if (ssl_io->verbose) {
+		/* This error should normally be logged by lib-ssl-iostream's
+		   caller. But if verbose=TRUE, log it here as well to make
+		   sure that the error is always logged. */
+		i_debug("%sSSL error: %s", ssl_io->log_prefix, new_str);
+	}
+	i_free(ssl_io->last_error);
+	ssl_io->last_error = new_str;
+}
+
+static void openssl_info_callback(const SSL *ssl, int where, int ret)
+{
+	struct ssl_iostream *ssl_io;
+
+	ssl_io = SSL_get_ex_data(ssl, dovecot_ssl_extdata_index);
+	if ((where & SSL_CB_ALERT) != 0) {
+		switch (ret & 0xff) {
+		case SSL_AD_CLOSE_NOTIFY:
+			i_debug("%sSSL alert: %s",
+				ssl_io->log_prefix,
+				SSL_alert_desc_string_long(ret));
+			break;
+		default:
+			i_debug("%sSSL alert: where=0x%x, ret=%d: %s %s",
+				ssl_io->log_prefix, where, ret,
+				SSL_alert_type_string_long(ret),
+				SSL_alert_desc_string_long(ret));
+			break;
+		}
+	} else if (ret == 0) {
+		i_debug("%sSSL failed: where=0x%x: %s",
+			ssl_io->log_prefix, where, SSL_state_string_long(ssl));
+	} else {
+		i_debug("%sSSL: where=0x%x, ret=%d: %s",
+			ssl_io->log_prefix, where, ret,
+			SSL_state_string_long(ssl));
+	}
+}
+
+static int
+openssl_iostream_use_certificate(struct ssl_iostream *ssl_io, const char *cert,
+				 const char **error_r)
+{
+	BIO *in;
+	X509 *x;
+	int ret = 0;
+
+	in = BIO_new_mem_buf(t_strdup_noconst(cert), strlen(cert));
+	if (in == NULL) {
+		*error_r = t_strdup_printf("BIO_new_mem_buf() failed: %s",
+					   openssl_iostream_error());
+		return -1;
+	}
+
+	x = PEM_read_bio_X509(in, NULL, NULL, NULL);
+	if (x != NULL) {
+		ret = SSL_use_certificate(ssl_io->ssl, x);
+		if (ERR_peek_error() != 0)
+			ret = 0;
+		X509_free(x);
+	}
+	BIO_free(in);
+
+	if (ret == 0) {
+		*error_r = t_strdup_printf("Can't load ssl_cert: %s",
+			openssl_iostream_use_certificate_error(cert, NULL));
+		return -1;
+	}
+	return 0;
+}
+
+static int
+openssl_iostream_use_key(struct ssl_iostream *ssl_io, const char *set_name,
+			 const struct ssl_iostream_cert *set,
+			 const char **error_r)
+{
+	EVP_PKEY *pkey;
+	int ret = 0;
+
+	if (openssl_iostream_load_key(set, set_name, &pkey, error_r) < 0)
+		return -1;
+	if (SSL_use_PrivateKey(ssl_io->ssl, pkey) != 1) {
+		*error_r = t_strdup_printf(
+			"Can't load SSL private key (%s setting): %s",
+			set_name, openssl_iostream_key_load_error());
+		ret = -1;
+	}
+	EVP_PKEY_free(pkey);
+	return ret;
+}
+
+static int
+openssl_iostream_verify_client_cert(int preverify_ok, X509_STORE_CTX *ctx)
+{
+	int ssl_extidx = SSL_get_ex_data_X509_STORE_CTX_idx();
+	SSL *ssl;
+	struct ssl_iostream *ssl_io;
+	char certname[1024];
+	X509_NAME *subject;
+
+	ssl = X509_STORE_CTX_get_ex_data(ctx, ssl_extidx);
+	ssl_io = SSL_get_ex_data(ssl, dovecot_ssl_extdata_index);
+	ssl_io->cert_received = TRUE;
+
+	subject = X509_get_subject_name(X509_STORE_CTX_get_current_cert(ctx));
+	if (subject == NULL ||
+	    X509_NAME_oneline(subject, certname, sizeof(certname)) == NULL)
+		certname[0] = '\0';
+	else
+		certname[sizeof(certname)-1] = '\0'; /* just in case.. */
+	if (preverify_ok == 0) {
+		openssl_iostream_set_error(ssl_io, t_strdup_printf(
+			"Received invalid SSL certificate: %s: %s (check %s)",
+			X509_verify_cert_error_string(X509_STORE_CTX_get_error(ctx)), certname,
+			ssl_io->ctx->client_ctx ?
+				"ssl_client_ca_* settings?" :
+				"ssl_ca setting?"));
+		if (ssl_io->verbose_invalid_cert)
+			i_info("%s", ssl_io->last_error);
+	} else if (ssl_io->verbose) {
+		i_info("Received valid SSL certificate: %s", certname);
+	}
+	if (preverify_ok == 0) {
+		ssl_io->cert_broken = TRUE;
+		if (!ssl_io->allow_invalid_cert) {
+			ssl_io->handshake_failed = TRUE;
+			return 0;
+		}
+	}
+	return 1;
+}
+
+static int
+openssl_iostream_set(struct ssl_iostream *ssl_io,
+		     const struct ssl_iostream_settings *set,
+		     const char **error_r)
+{
+	const struct ssl_iostream_settings *ctx_set = &ssl_io->ctx->set;
+	int verify_flags;
+
+	if (set->verbose)
+		SSL_set_info_callback(ssl_io->ssl, openssl_info_callback);
+
+       if (set->cipher_list != NULL &&
+	    strcmp(ctx_set->cipher_list, set->cipher_list) != 0) {
+		if (SSL_set_cipher_list(ssl_io->ssl, set->cipher_list) == 0) {
+			*error_r = t_strdup_printf(
+				"Can't set cipher list to '%s': %s",
+				set->cipher_list, openssl_iostream_error());
+			return -1;
+		}
+	}
+#ifdef HAVE_SSL_CTX_SET1_CURVES_LIST
+	if (set->curve_list != NULL && strlen(set->curve_list) > 0 &&
+		(ctx_set->curve_list == NULL || strcmp(ctx_set->curve_list, set->curve_list) != 0)) {
+		if (SSL_set1_curves_list(ssl_io->ssl, set->curve_list) == 0) {
+			*error_r = t_strdup_printf(
+					"Failed to set curve list to '%s'",
+					set->curve_list);
+			return -1;
+		}
+	}
+#endif
+#ifdef HAVE_SSL_CTX_SET_CIPHERSUITES
+        if (set->ciphersuites != NULL &&
+	    strcmp(ctx_set->ciphersuites, set->ciphersuites) != 0) {
+		if (SSL_set_ciphersuites(ssl_io->ssl, set->ciphersuites) == 0) {
+			*error_r = t_strdup_printf(
+				"Can't set ciphersuites to '%s': %s",
+				set->ciphersuites, openssl_iostream_error());
+			return -1;
+		}
+	}
+#endif
+	if (set->prefer_server_ciphers)
+		SSL_set_options(ssl_io->ssl, SSL_OP_CIPHER_SERVER_PREFERENCE);
+	if (set->min_protocol != NULL) {
+#if defined(HAVE_SSL_CLEAR_OPTIONS)
+		SSL_clear_options(ssl_io->ssl, OPENSSL_ALL_PROTOCOL_OPTIONS);
+#endif
+		long opts;
+		int min_protocol;
+		if (openssl_min_protocol_to_options(set->min_protocol, &opts,
+						    &min_protocol) < 0) {
+			*error_r = t_strdup_printf(
+					"Unknown ssl_min_protocol setting '%s'",
+					set->min_protocol);
+			return -1;
+		}
+#ifdef HAVE_SSL_CTX_SET_MIN_PROTO_VERSION
+		SSL_set_min_proto_version(ssl_io->ssl, min_protocol);
+#else
+		SSL_set_options(ssl_io->ssl, opts);
+#endif
+	}
+
+	if (set->cert.cert != NULL && strcmp(ctx_set->cert.cert, set->cert.cert) != 0) {
+		if (openssl_iostream_use_certificate(ssl_io, set->cert.cert, error_r) < 0)
+			return -1;
+	}
+	if (set->cert.key != NULL && strcmp(ctx_set->cert.key, set->cert.key) != 0) {
+		if (openssl_iostream_use_key(ssl_io, "ssl_key", &set->cert, error_r) < 0)
+			return -1;
+	}
+	if (set->alt_cert.cert != NULL && strcmp(ctx_set->alt_cert.cert, set->alt_cert.cert) != 0) {
+		if (openssl_iostream_use_certificate(ssl_io, set->alt_cert.cert, error_r) < 0)
+			return -1;
+	}
+	if (set->alt_cert.key != NULL && strcmp(ctx_set->alt_cert.key, set->alt_cert.key) != 0) {
+		if (openssl_iostream_use_key(ssl_io, "ssl_alt_key", &set->alt_cert, error_r) < 0)
+			return -1;
+	}
+	if (set->verify_remote_cert) {
+		if (ssl_io->ctx->client_ctx)
+			verify_flags = SSL_VERIFY_NONE;
+		else
+			verify_flags = SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE;
+		SSL_set_verify(ssl_io->ssl, verify_flags,
+			       openssl_iostream_verify_client_cert);
+	}
+
+	if (set->cert_username_field != NULL) {
+		ssl_io->username_nid = OBJ_txt2nid(set->cert_username_field);
+		if (ssl_io->username_nid == NID_undef) {
+			*error_r = t_strdup_printf(
+				"Invalid cert_username_field: %s",
+				set->cert_username_field);
+			return -1;
+		}
+	} else {
+		ssl_io->username_nid = ssl_io->ctx->username_nid;
+	}
+
+	ssl_io->verbose = set->verbose;
+	ssl_io->verbose_invalid_cert = set->verbose_invalid_cert || set->verbose;
+	ssl_io->allow_invalid_cert = set->allow_invalid_cert;
+	return 0;
+}
+
+static int
+openssl_iostream_create(struct ssl_iostream_context *ctx, const char *host,
+			const struct ssl_iostream_settings *set,
+			struct istream **input, struct ostream **output,
+			struct ssl_iostream **iostream_r,
+			const char **error_r)
+{
+	struct ssl_iostream *ssl_io;
+	SSL *ssl;
+	BIO *bio_int, *bio_ext;
+
+	/* Don't allow an existing io_add_istream() to be use on the input.
+	   It would seem to work, but it would also cause hangs. */
+	i_assert(i_stream_get_root_io(*input)->real_stream->io == NULL);
+
+	ssl = SSL_new(ctx->ssl_ctx);
+	if (ssl == NULL) {
+		*error_r = t_strdup_printf("SSL_new() failed: %s",
+					   openssl_iostream_error());
+		return -1;
+	}
+
+	/* BIO pairs use default buffer sizes (17 kB in OpenSSL 0.9.8e).
+	   Each of the BIOs have one "write buffer". BIO_write() copies data
+	   to them, while BIO_read() reads from the other BIO's write buffer
+	   into the given buffer. The bio_int is used by OpenSSL and bio_ext
+	   is used by this library. */
+	if (BIO_new_bio_pair(&bio_int, 0, &bio_ext, 0) != 1) {
+		*error_r = t_strdup_printf("BIO_new_bio_pair() failed: %s",
+					   openssl_iostream_error());
+		SSL_free(ssl);
+		return -1;
+	}
+
+	ssl_io = i_new(struct ssl_iostream, 1);
+	ssl_io->refcount = 1;
+	ssl_io->ctx = ctx;
+	ssl_iostream_context_ref(ssl_io->ctx);
+	ssl_io->ssl = ssl;
+	ssl_io->bio_ext = bio_ext;
+	ssl_io->plain_input = *input;
+	ssl_io->plain_output = *output;
+	ssl_io->connected_host = i_strdup(host);
+	ssl_io->log_prefix = host == NULL ? i_strdup("") :
+		i_strdup_printf("%s: ", host);
+	/* bio_int will be freed by SSL_free() */
+	SSL_set_bio(ssl_io->ssl, bio_int, bio_int);
+        SSL_set_ex_data(ssl_io->ssl, dovecot_ssl_extdata_index, ssl_io);
+#ifdef HAVE_SSL_GET_SERVERNAME
+	SSL_set_tlsext_host_name(ssl_io->ssl, host);
+#endif
+
+	if (openssl_iostream_set(ssl_io, set, error_r) < 0) {
+		openssl_iostream_free(ssl_io);
+		return -1;
+	}
+
+	o_stream_uncork(ssl_io->plain_output);
+
+	*input = openssl_i_stream_create_ssl(ssl_io);
+	ssl_io->ssl_input = *input;
+
+	*output = openssl_o_stream_create_ssl(ssl_io);
+	i_stream_set_name(*input, t_strconcat("SSL ",
+		i_stream_get_name(ssl_io->plain_input), NULL));
+	o_stream_set_name(*output, t_strconcat("SSL ",
+		o_stream_get_name(ssl_io->plain_output), NULL));
+
+	if (ssl_io->plain_output->real_stream->error_handling_disabled)
+		o_stream_set_no_error_handling(*output, TRUE);
+
+	ssl_io->ssl_output = *output;
+	*iostream_r = ssl_io;
+	return 0;
+}
+
+static void openssl_iostream_free(struct ssl_iostream *ssl_io)
+{
+	ssl_iostream_context_unref(&ssl_io->ctx);
+	o_stream_unref(&ssl_io->plain_output);
+	i_stream_unref(&ssl_io->plain_input);
+	BIO_free(ssl_io->bio_ext);
+	SSL_free(ssl_io->ssl);
+	i_free(ssl_io->plain_stream_errstr);
+	i_free(ssl_io->last_error);
+	i_free(ssl_io->connected_host);
+	i_free(ssl_io->sni_host);
+	i_free(ssl_io->log_prefix);
+	i_free(ssl_io);
+}
+
+static void openssl_iostream_unref(struct ssl_iostream *ssl_io)
+{
+	i_assert(ssl_io->refcount > 0);
+	if (--ssl_io->refcount > 0)
+		return;
+
+	openssl_iostream_free(ssl_io);
+}
+
+void openssl_iostream_shutdown(struct ssl_iostream *ssl_io)
+{
+	if (ssl_io->destroyed)
+		return;
+
+	i_assert(ssl_io->ssl_input != NULL);
+	i_assert(ssl_io->ssl_output != NULL);
+
+	ssl_io->destroyed = TRUE;
+	if (ssl_io->handshaked && SSL_shutdown(ssl_io->ssl) != 1) {
+		/* if bidirectional shutdown fails we need to clear
+		   the error queue */
+		openssl_iostream_clear_errors();
+	}
+	if (ssl_io->handshaked) {
+		(void)openssl_iostream_bio_sync(ssl_io,
+			OPENSSL_IOSTREAM_SYNC_TYPE_WRITE);
+	}
+	(void)o_stream_flush(ssl_io->plain_output);
+	/* close the plain i/o streams, because their fd may be closed soon,
+	   but we may still keep this ssl-iostream referenced until later. */
+	i_stream_close(ssl_io->plain_input);
+	o_stream_close(ssl_io->plain_output);
+}
+
+static void openssl_iostream_destroy(struct ssl_iostream *ssl_io)
+{
+	openssl_iostream_shutdown(ssl_io);
+	ssl_iostream_unref(&ssl_io);
+}
+
+static int openssl_iostream_bio_output_real(struct ssl_iostream *ssl_io)
+{
+	size_t bytes, max_bytes = 0;
+	ssize_t sent;
+	unsigned char buffer[IO_BLOCK_SIZE];
+	int result = 0;
+	int ret;
+
+	o_stream_cork(ssl_io->plain_output);
+	while ((bytes = BIO_ctrl_pending(ssl_io->bio_ext)) > 0) {
+		/* bytes contains how many SSL encrypted bytes we should be
+		   sending out */
+		max_bytes = o_stream_get_buffer_avail_size(ssl_io->plain_output);
+		if (bytes > max_bytes) {
+			if (max_bytes == 0) {
+				/* wait until output buffer clears */
+				break;
+			}
+			bytes = max_bytes;
+		}
+		if (bytes > sizeof(buffer))
+			bytes = sizeof(buffer);
+
+		/* BIO_read() is guaranteed to return all the bytes that
+		   BIO_ctrl_pending() returned */
+		ret = BIO_read(ssl_io->bio_ext, buffer, bytes);
+		i_assert(ret == (int)bytes);
+
+		/* we limited number of read bytes to plain_output's
+		   available size. this send() is guaranteed to either
+		   fully succeed or completely fail due to some error. */
+		sent = o_stream_send(ssl_io->plain_output, buffer, bytes);
+		if (sent < 0) {
+			o_stream_uncork(ssl_io->plain_output);
+			return -1;
+		}
+		i_assert(sent == (ssize_t)bytes);
+		result = 1;
+	}
+
+	ret = o_stream_uncork_flush(ssl_io->plain_output);
+	if (ret < 0)
+		return -1;
+	if (ret == 0 || (bytes > 0 && max_bytes == 0))
+		o_stream_set_flush_pending(ssl_io->plain_output, TRUE);
+
+	return result;
+}
+
+static int openssl_iostream_bio_output(struct ssl_iostream *ssl_io)
+{
+	int ret;
+
+	ret = openssl_iostream_bio_output_real(ssl_io);
+	if (ret < 0) {
+		i_assert(ssl_io->plain_output->stream_errno != 0);
+		i_free(ssl_io->plain_stream_errstr);
+		ssl_io->plain_stream_errstr =
+			i_strdup(o_stream_get_error(ssl_io->plain_output));
+		ssl_io->plain_stream_errno =
+			ssl_io->plain_output->stream_errno;
+		ssl_io->closed = TRUE;
+	}
+	return ret;
+}
+
+static ssize_t
+openssl_iostream_read_more(struct ssl_iostream *ssl_io,
+			   enum openssl_iostream_sync_type type, size_t wanted,
+			   const unsigned char **data_r, size_t *size_r)
+{
+	*data_r = i_stream_get_data(ssl_io->plain_input, size_r);
+	if (*size_r > 0)
+		return 0;
+
+	if (type == OPENSSL_IOSTREAM_SYNC_TYPE_CONTINUE_READ) {
+		/* only the first i_stream_read() call attempts to read more
+		   input. the following reads will just process the buffered
+		   data. */
+		return 0;
+	}
+
+	if (i_stream_read_limited(ssl_io->plain_input, data_r, size_r,
+				  wanted) < 0)
+		return -1;
+	return 0;
+}
+
+static int
+openssl_iostream_bio_input(struct ssl_iostream *ssl_io,
+			   enum openssl_iostream_sync_type type)
+{
+	const unsigned char *data;
+	size_t bytes, size;
+	int ret;
+	bool bytes_read = FALSE;
+
+	while ((bytes = BIO_ctrl_get_write_guarantee(ssl_io->bio_ext)) > 0) {
+		/* bytes contains how many bytes we can write to bio_ext */
+		ret = openssl_iostream_read_more(ssl_io, type, bytes,
+						 &data, &size);
+		if (ret == -1 && size == 0 && !bytes_read) {
+			if (ssl_io->plain_input->stream_errno != 0) {
+				i_free(ssl_io->plain_stream_errstr);
+				ssl_io->plain_stream_errstr =
+					i_strdup(i_stream_get_error(ssl_io->plain_input));
+				ssl_io->plain_stream_errno =
+					ssl_io->plain_input->stream_errno;
+			}
+			ssl_io->closed = TRUE;
+			return -1;
+		}
+		if (size == 0) {
+			/* wait for more input */
+			break;
+		}
+		if (size > bytes)
+			size = bytes;
+
+		ret = BIO_write(ssl_io->bio_ext, data, size);
+		i_assert(ret == (ssize_t)size);
+
+		i_stream_skip(ssl_io->plain_input, size);
+		bytes_read = TRUE;
+	}
+	if (bytes == 0 && !bytes_read && ssl_io->want_read) {
+		/* shouldn't happen */
+		i_error("SSL BIO buffer size too small");
+		i_free(ssl_io->plain_stream_errstr);
+		ssl_io->plain_stream_errstr =
+			i_strdup("SSL BIO buffer size too small");
+		ssl_io->plain_stream_errno = EINVAL;
+		ssl_io->closed = TRUE;
+		return -1;
+	}
+	if (bytes_read) {
+		if (ssl_io->ostream_flush_waiting_input) {
+			ssl_io->ostream_flush_waiting_input = FALSE;
+			o_stream_set_flush_pending(ssl_io->plain_output, TRUE);
+		}
+	}
+	if (bytes_read || i_stream_get_data_size(ssl_io->plain_input) > 0) {
+		if (i_stream_get_data_size(ssl_io->plain_input) > 0 ||
+		    (type != OPENSSL_IOSTREAM_SYNC_TYPE_FIRST_READ &&
+		     type != OPENSSL_IOSTREAM_SYNC_TYPE_CONTINUE_READ))
+			i_stream_set_input_pending(ssl_io->ssl_input, TRUE);
+		ssl_io->want_read = FALSE;
+	}
+	return (bytes_read ? 1 : 0);
+}
+
+int openssl_iostream_bio_sync(struct ssl_iostream *ssl_io,
+			      enum openssl_iostream_sync_type type)
+{
+	int ret;
+
+	i_assert(type != OPENSSL_IOSTREAM_SYNC_TYPE_NONE);
+
+	ret = openssl_iostream_bio_output(ssl_io);
+	if (ret >= 0 && openssl_iostream_bio_input(ssl_io, type) > 0)
+		ret = 1;
+	return ret;
+}
+
+static void openssl_iostream_closed(struct ssl_iostream *ssl_io)
+{
+	if (ssl_io->plain_stream_errno != 0) {
+		i_assert(ssl_io->plain_stream_errstr != NULL);
+		openssl_iostream_set_error(ssl_io, ssl_io->plain_stream_errstr);
+		errno = ssl_io->plain_stream_errno;
+	} else {
+		openssl_iostream_set_error(ssl_io, "Connection closed");
+		errno = EPIPE;
+	}
+}
+
+int openssl_iostream_handle_error(struct ssl_iostream *ssl_io, int ret,
+				  enum openssl_iostream_sync_type type,
+				  const char *func_name)
+{
+	const char *errstr = NULL;
+	int err;
+
+	err = SSL_get_error(ssl_io->ssl, ret);
+	switch (err) {
+	case SSL_ERROR_WANT_WRITE:
+		if (type != OPENSSL_IOSTREAM_SYNC_TYPE_NONE &&
+		    openssl_iostream_bio_sync(ssl_io, type) == 0) {
+			if (type != OPENSSL_IOSTREAM_SYNC_TYPE_WRITE)
+				i_panic("SSL ostream buffer size not unlimited");
+			return 0;
+		}
+		if (ssl_io->closed) {
+			openssl_iostream_closed(ssl_io);
+			return -1;
+		}
+		if (type == OPENSSL_IOSTREAM_SYNC_TYPE_NONE)
+			return 0;
+		return 1;
+	case SSL_ERROR_WANT_READ:
+		ssl_io->want_read = TRUE;
+		if (type != OPENSSL_IOSTREAM_SYNC_TYPE_NONE)
+			(void)openssl_iostream_bio_sync(ssl_io, type);
+		if (ssl_io->closed) {
+			openssl_iostream_closed(ssl_io);
+			return -1;
+		}
+		if (type == OPENSSL_IOSTREAM_SYNC_TYPE_NONE)
+			return 0;
+		return ssl_io->want_read ? 0 : 1;
+	case SSL_ERROR_SYSCALL:
+		/* eat up the error queue */
+		if (ERR_peek_error() != 0) {
+			errstr = openssl_iostream_error();
+			errno = EINVAL;
+		} else if (ret == 0) {
+			/* EOF. */
+			errno = EPIPE;
+			errstr = "Disconnected";
+			break;
+		} else if (errno != 0) {
+			errstr = strerror(errno);
+		} else {
+			/* Seen this at least with v1.1.0l SSL_accept() */
+			errstr = "OpenSSL BUG: errno=0";
+			errno = EINVAL;
+		}
+		errstr = t_strdup_printf("%s syscall failed: %s",
+					 func_name, errstr);
+		break;
+	case SSL_ERROR_ZERO_RETURN:
+		/* clean connection closing */
+		errno = EPIPE;
+		if (ssl_io->handshaked)
+			i_free_and_null(ssl_io->last_error);
+		else if (ssl_io->last_error == NULL) {
+			errstr = "SSL connection closed during handshake";
+			break;
+		}
+		return -1;
+	case SSL_ERROR_SSL:
+		errstr = t_strdup_printf("%s failed: %s",
+					 func_name, openssl_iostream_error());
+		errno = EINVAL;
+		break;
+	default:
+		errstr = t_strdup_printf("%s failed: unknown failure %d (%s)",
+					 func_name, err,
+					 openssl_iostream_error());
+		errno = EINVAL;
+		break;
+	}
+
+	openssl_iostream_set_error(ssl_io, errstr);
+	return -1;
+}
+
+static bool
+openssl_iostream_cert_match_name(struct ssl_iostream *ssl_io,
+				 const char *verify_name, const char **reason_r)
+{
+	if (!ssl_iostream_has_valid_client_cert(ssl_io)) {
+		*reason_r = "Invalid certificate";
+		return FALSE;
+	}
+
+	return openssl_cert_match_name(ssl_io->ssl, verify_name, reason_r);
+}
+
+static int openssl_iostream_handshake(struct ssl_iostream *ssl_io)
+{
+	const char *reason, *error = NULL;
+	int ret;
+
+	i_assert(!ssl_io->handshaked);
+
+	/* we are being destroyed, so do not do any more handshaking */
+	if (ssl_io->destroyed)
+		return 0;
+
+	if (ssl_io->ctx->client_ctx) {
+		while ((ret = SSL_connect(ssl_io->ssl)) <= 0) {
+			ret = openssl_iostream_handle_error(ssl_io, ret,
+				OPENSSL_IOSTREAM_SYNC_TYPE_HANDSHAKE, "SSL_connect()");
+			if (ret <= 0)
+				return ret;
+		}
+	} else {
+		while ((ret = SSL_accept(ssl_io->ssl)) <= 0) {
+			ret = openssl_iostream_handle_error(ssl_io, ret,
+				OPENSSL_IOSTREAM_SYNC_TYPE_HANDSHAKE, "SSL_accept()");
+			if (ret <= 0)
+				return ret;
+		}
+	}
+	/* handshake finished */
+	(void)openssl_iostream_bio_sync(ssl_io, OPENSSL_IOSTREAM_SYNC_TYPE_HANDSHAKE);
+
+	if (ssl_io->handshake_callback != NULL) {
+		if (ssl_io->handshake_callback(&error, ssl_io->handshake_context) < 0) {
+			i_assert(error != NULL);
+			openssl_iostream_set_error(ssl_io, error);
+			ssl_io->handshake_failed = TRUE;
+		}
+       } else if (ssl_io->connected_host != NULL && !ssl_io->handshake_failed &&
+		  !ssl_io->allow_invalid_cert) {
+		if (ssl_iostream_check_cert_validity(ssl_io, ssl_io->connected_host, &reason) < 0) {
+			openssl_iostream_set_error(ssl_io, reason);
+			ssl_io->handshake_failed = TRUE;
+		}
+	}
+	if (ssl_io->handshake_failed) {
+		i_stream_close(ssl_io->plain_input);
+		o_stream_close(ssl_io->plain_output);
+		errno = EINVAL;
+		return -1;
+	}
+	i_free_and_null(ssl_io->last_error);
+	ssl_io->handshaked = TRUE;
+
+	if (ssl_io->ssl_output != NULL)
+		(void)o_stream_flush(ssl_io->ssl_output);
+	return 1;
+}
+
+static void
+openssl_iostream_set_handshake_callback(struct ssl_iostream *ssl_io,
+					ssl_iostream_handshake_callback_t *callback,
+					void *context)
+{
+	ssl_io->handshake_callback = callback;
+	ssl_io->handshake_context = context;
+}
+
+static void
+openssl_iostream_set_sni_callback(struct ssl_iostream *ssl_io,
+				  ssl_iostream_sni_callback_t *callback,
+				  void *context)
+{
+	ssl_io->sni_callback = callback;
+	ssl_io->sni_context = context;
+}
+
+static void
+openssl_iostream_change_context(struct ssl_iostream *ssl_io,
+				struct ssl_iostream_context *ctx)
+{
+	if (ctx != ssl_io->ctx) {
+		SSL_set_SSL_CTX(ssl_io->ssl, ctx->ssl_ctx);
+		ssl_iostream_context_ref(ctx);
+		ssl_iostream_context_unref(&ssl_io->ctx);
+		ssl_io->ctx = ctx;
+	}
+}
+
+static void openssl_iostream_set_log_prefix(struct ssl_iostream *ssl_io,
+					    const char *prefix)
+{
+	i_free(ssl_io->log_prefix);
+	ssl_io->log_prefix = i_strdup(prefix);
+}
+
+static bool openssl_iostream_is_handshaked(const struct ssl_iostream *ssl_io)
+{
+	return ssl_io->handshaked;
+}
+
+static bool
+openssl_iostream_has_handshake_failed(const struct ssl_iostream *ssl_io)
+{
+	return ssl_io->handshake_failed;
+}
+
+static bool
+openssl_iostream_has_valid_client_cert(const struct ssl_iostream *ssl_io)
+{
+	return ssl_io->cert_received && !ssl_io->cert_broken;
+}
+
+static bool
+openssl_iostream_has_broken_client_cert(struct ssl_iostream *ssl_io)
+{
+	return ssl_io->cert_received && ssl_io->cert_broken;
+}
+
+static const char *
+openssl_iostream_get_peer_name(struct ssl_iostream *ssl_io)
+{
+	X509 *x509;
+	char *name;
+	int len;
+
+	if (!ssl_iostream_has_valid_client_cert(ssl_io))
+		return NULL;
+
+	x509 = SSL_get_peer_certificate(ssl_io->ssl);
+	i_assert(x509 != NULL);
+
+	len = X509_NAME_get_text_by_NID(X509_get_subject_name(x509),
+					ssl_io->username_nid, NULL, 0);
+	if (len < 0)
+		name = "";
+	else {
+		name = t_malloc0(len + 1);
+		if (X509_NAME_get_text_by_NID(X509_get_subject_name(x509),
+					      ssl_io->username_nid,
+					      name, len + 1) < 0)
+			name = "";
+		else if (strlen(name) != (size_t)len) {
+			/* NUL characters in name. Someone's trying to fake
+			   being another user? Don't allow it. */
+			name = "";
+		}
+	}
+	X509_free(x509);
+	
+	return *name == '\0' ? NULL : name;
+}
+
+static const char *openssl_iostream_get_server_name(struct ssl_iostream *ssl_io)
+{
+	return ssl_io->sni_host;
+}
+
+static const char *
+openssl_iostream_get_compression(struct ssl_iostream *ssl_io)
+{
+#if defined(HAVE_SSL_COMPRESSION) && !defined(OPENSSL_NO_COMP)
+	const COMP_METHOD *comp;
+
+	comp = SSL_get_current_compression(ssl_io->ssl);
+	return comp == NULL ? NULL : SSL_COMP_get_name(comp);
+#else
+	return NULL;
+#endif
+}
+
+static const char *
+openssl_iostream_get_security_string(struct ssl_iostream *ssl_io)
+{
+	const SSL_CIPHER *cipher;
+#if defined(HAVE_SSL_COMPRESSION) && !defined(OPENSSL_NO_COMP)
+	const COMP_METHOD *comp;
+#endif
+	const char *comp_str;
+	int bits, alg_bits;
+
+	if (!ssl_io->handshaked)
+		return "";
+
+	cipher = SSL_get_current_cipher(ssl_io->ssl);
+	bits = SSL_CIPHER_get_bits(cipher, &alg_bits);
+#if defined(HAVE_SSL_COMPRESSION) && !defined(OPENSSL_NO_COMP)
+	comp = SSL_get_current_compression(ssl_io->ssl);
+	comp_str = comp == NULL ? "" :
+		t_strconcat(" ", SSL_COMP_get_name(comp), NULL);
+#else
+	comp_str = "";
+#endif
+	return t_strdup_printf("%s with cipher %s (%d/%d bits)%s",
+			       SSL_get_version(ssl_io->ssl),
+			       SSL_CIPHER_get_name(cipher),
+			       bits, alg_bits, comp_str);
+}
+
+static const char *
+openssl_iostream_get_last_error(struct ssl_iostream *ssl_io)
+{
+	return ssl_io->last_error;
+}
+
+static const char *
+openssl_iostream_get_cipher(struct ssl_iostream *ssl_io, unsigned int *bits_r)
+{
+	if (!ssl_io->handshaked)
+		return NULL;
+
+	const SSL_CIPHER *cipher = SSL_get_current_cipher(ssl_io->ssl);
+	*bits_r = SSL_CIPHER_get_bits(cipher, NULL);
+	return SSL_CIPHER_get_name(cipher);
+}
+
+static const char *
+openssl_iostream_get_pfs(struct ssl_iostream *ssl_io)
+{
+	if (!ssl_io->handshaked)
+		return NULL;
+
+	const SSL_CIPHER *cipher = SSL_get_current_cipher(ssl_io->ssl);
+#if defined(HAVE_SSL_CIPHER_get_kx_nid)
+	int nid = SSL_CIPHER_get_kx_nid(cipher);
+	return OBJ_nid2sn(nid);
+#else
+	char buf[128];
+	const char *desc, *ptr;
+	if ((desc = SSL_CIPHER_description(cipher, buf, sizeof(buf)))==NULL ||
+	    (ptr = strstr(desc, "Kx=")) == NULL)
+		return "";
+	return t_strcut(ptr+3, ' ');
+#endif
+}
+
+static const char *
+openssl_iostream_get_protocol_name(struct ssl_iostream *ssl_io)
+{
+	if (!ssl_io->handshaked)
+		return NULL;
+	return SSL_get_version(ssl_io->ssl);
+}
+
+
+static const struct iostream_ssl_vfuncs ssl_vfuncs = {
+	.global_init = openssl_iostream_global_init,
+	.context_init_client = openssl_iostream_context_init_client,
+	.context_init_server = openssl_iostream_context_init_server,
+	.context_ref = openssl_iostream_context_ref,
+	.context_unref = openssl_iostream_context_unref,
+
+	.create = openssl_iostream_create,
+	.unref = openssl_iostream_unref,
+	.destroy = openssl_iostream_destroy,
+
+	.handshake = openssl_iostream_handshake,
+	.set_handshake_callback = openssl_iostream_set_handshake_callback,
+	.set_sni_callback = openssl_iostream_set_sni_callback,
+	.change_context = openssl_iostream_change_context,
+
+	.set_log_prefix = openssl_iostream_set_log_prefix,
+	.is_handshaked = openssl_iostream_is_handshaked,
+	.has_handshake_failed = openssl_iostream_has_handshake_failed,
+	.has_valid_client_cert = openssl_iostream_has_valid_client_cert,
+	.has_broken_client_cert = openssl_iostream_has_broken_client_cert,
+	.cert_match_name = openssl_iostream_cert_match_name,
+	.get_peer_name = openssl_iostream_get_peer_name,
+	.get_server_name = openssl_iostream_get_server_name,
+	.get_compression = openssl_iostream_get_compression,
+	.get_security_string = openssl_iostream_get_security_string,
+	.get_last_error = openssl_iostream_get_last_error,
+	.get_cipher = openssl_iostream_get_cipher,
+	.get_pfs = openssl_iostream_get_pfs,
+	.get_protocol_name = openssl_iostream_get_protocol_name,
+};
+
+void ssl_iostream_openssl_init(void)
+{
+	unsigned char buf;
+	if (RAND_bytes(&buf, 1) < 1)
+		i_fatal("OpenSSL RNG failed to initialize");
+	iostream_ssl_module_init(&ssl_vfuncs);
+}
+
+void ssl_iostream_openssl_deinit(void)
+{
+	openssl_iostream_global_deinit();
+}
diff --git a/src/lib-ssl-iostream/iostream-openssl.h b/src/lib-ssl-iostream/iostream-openssl.h
new file mode 100644
index 0000000..4449668
--- /dev/null
+++ b/src/lib-ssl-iostream/iostream-openssl.h
@@ -0,0 +1,129 @@
+#ifndef IOSTREAM_OPENSSL_H
+#define IOSTREAM_OPENSSL_H
+
+#include "iostream-ssl-private.h"
+
+#include <openssl/ssl.h>
+
+#ifndef HAVE_ASN1_STRING_GET0_DATA
+#  define ASN1_STRING_get0_data(str) ASN1_STRING_data(str)
+#endif
+enum openssl_iostream_sync_type {
+	OPENSSL_IOSTREAM_SYNC_TYPE_NONE,
+	OPENSSL_IOSTREAM_SYNC_TYPE_FIRST_READ,
+	OPENSSL_IOSTREAM_SYNC_TYPE_CONTINUE_READ,
+	OPENSSL_IOSTREAM_SYNC_TYPE_WRITE,
+	OPENSSL_IOSTREAM_SYNC_TYPE_HANDSHAKE
+};
+
+struct ssl_iostream_context {
+	int refcount;
+	SSL_CTX *ssl_ctx;
+
+	pool_t pool;
+	struct ssl_iostream_settings set;
+
+	int username_nid;
+
+	bool client_ctx:1;
+};
+
+struct ssl_iostream {
+	int refcount;
+	struct ssl_iostream_context *ctx;
+
+	SSL *ssl;
+	BIO *bio_ext;
+
+	struct istream *plain_input;
+	struct ostream *plain_output;
+	struct istream *ssl_input;
+	struct ostream *ssl_output;
+
+	/* SSL clients: host where we connected to */
+	char *connected_host;
+	/* SSL servers: host requested by the client via SNI */
+	char *sni_host;
+	char *last_error;
+	char *log_prefix;
+	char *plain_stream_errstr;
+	int plain_stream_errno;
+
+	/* copied settings */
+	bool verbose, verbose_invalid_cert, allow_invalid_cert;
+	int username_nid;
+
+	ssl_iostream_handshake_callback_t *handshake_callback;
+	void *handshake_context;
+
+	ssl_iostream_sni_callback_t *sni_callback;
+	void *sni_context;
+
+	bool handshaked:1;
+	bool handshake_failed:1;
+	bool cert_received:1;
+	bool cert_broken:1;
+	bool want_read:1;
+	bool ostream_flush_waiting_input:1;
+	bool closed:1;
+	bool destroyed:1;
+};
+
+extern int dovecot_ssl_extdata_index;
+
+struct istream *openssl_i_stream_create_ssl(struct ssl_iostream *ssl_io);
+struct ostream *openssl_o_stream_create_ssl(struct ssl_iostream *ssl_io);
+
+int openssl_iostream_global_init(const struct ssl_iostream_settings *set,
+				 const char **error_r);
+
+int openssl_iostream_context_init_client(const struct ssl_iostream_settings *set,
+					 struct ssl_iostream_context **ctx_r,
+					 const char **error_r);
+int openssl_iostream_context_init_server(const struct ssl_iostream_settings *set,
+					 struct ssl_iostream_context **ctx_r,
+					 const char **error_r);
+void openssl_iostream_context_ref(struct ssl_iostream_context *ctx);
+void openssl_iostream_context_unref(struct ssl_iostream_context *ctx);
+void openssl_iostream_global_deinit(void);
+
+int openssl_iostream_load_key(const struct ssl_iostream_cert *set,
+			      const char *set_name,
+			      EVP_PKEY **pkey_r, const char **error_r);
+bool openssl_cert_match_name(SSL *ssl, const char *verify_name,
+			     const char **reason_r);
+#define OPENSSL_ALL_PROTOCOL_OPTIONS \
+	(SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3 | SSL_OP_NO_TLSv1)
+/* opt_r is used with SSL_set_options() and version_r is used with
+   SSL_set_min_proto_version(). Using either method should enable the same SSL
+   protocol versions. */
+int openssl_min_protocol_to_options(const char *min_protocol, long *opt_r,
+				    int *version_r) ATTR_NULL(2,3);
+
+/* Sync plain_input/plain_output streams with BIOs. Returns 1 if at least
+   one byte was read/written, 0 if nothing was written, and -1 if an error
+   occurred. */
+int openssl_iostream_bio_sync(struct ssl_iostream *ssl_io,
+			      enum openssl_iostream_sync_type type);
+
+/* Returns 1 if the operation should be retried (we read/wrote more data),
+   0 if the operation should retried later once more data has been
+   read/written, -1 if a fatal error occurred (errno is set). */
+int openssl_iostream_handle_error(struct ssl_iostream *ssl_io, int ret,
+				  enum openssl_iostream_sync_type type,
+				  const char *func_name);
+
+/* Perform clean shutdown for the connection. */
+void openssl_iostream_shutdown(struct ssl_iostream *ssl_io);
+
+void openssl_iostream_set_error(struct ssl_iostream *ssl_io, const char *str);
+const char *openssl_iostream_error(void);
+const char *openssl_iostream_key_load_error(void);
+const char *
+openssl_iostream_use_certificate_error(const char *cert, const char *set_name);
+void openssl_iostream_clear_errors(void);
+
+void ssl_iostream_openssl_init(void);
+void ssl_iostream_openssl_deinit(void);
+
+#endif
diff --git a/src/lib-ssl-iostream/iostream-ssl-context-cache.c b/src/lib-ssl-iostream/iostream-ssl-context-cache.c
new file mode 100644
index 0000000..a7245ce
--- /dev/null
+++ b/src/lib-ssl-iostream/iostream-ssl-context-cache.c
@@ -0,0 +1,129 @@
+/* Copyright (c) 2017-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "hash.h"
+#include "iostream-ssl-private.h"
+
+struct ssl_iostream_context_cache {
+	bool server;
+	struct ssl_iostream_settings set;
+};
+
+static pool_t ssl_iostream_contexts_pool;
+static HASH_TABLE(struct ssl_iostream_context_cache *,
+		  struct ssl_iostream_context *) ssl_iostream_contexts;
+
+static unsigned int
+ssl_iostream_context_cache_hash(const struct ssl_iostream_context_cache *cache)
+{
+	unsigned int n, i, g, h = 0;
+	const char *const cert[] = { cache->set.cert.cert, cache->set.alt_cert.cert };
+
+	/* checking for different certs is typically good enough,
+	   and it should be enough to check only the first few bytes (after the
+	   "BEGIN CERTIFICATE" line). */
+	for (n = 0; n < N_ELEMENTS(cert); n++) {
+		if (cert[n] == NULL)
+			continue;
+
+		for (i = 0; i < 64 && cert[n][i] != '\0'; i++) {
+			h = (h << 4) + cert[n][i];
+			if ((g = h & 0xf0000000UL) != 0) {
+				h = h ^ (g >> 24);
+				h = h ^ g;
+			}
+		}
+	}
+	return h ^ (cache->server ? 1 : 0);
+}
+
+static int
+ssl_iostream_context_cache_cmp(const struct ssl_iostream_context_cache *c1,
+			       const struct ssl_iostream_context_cache *c2)
+{
+	if (c1->server != c2->server)
+		return -1;
+	return ssl_iostream_settings_equals(&c1->set, &c2->set) ? 0 : -1;
+}
+
+static int
+ssl_iostream_context_cache_get(const struct ssl_iostream_settings *set,
+			       bool server,
+			       struct ssl_iostream_context **ctx_r,
+			       const char **error_r)
+{
+	struct ssl_iostream_context *ctx;
+	struct ssl_iostream_context_cache *cache;
+	struct ssl_iostream_context_cache lookup = {
+		.server = server,
+		.set = *set,
+	};
+
+	if (ssl_iostream_contexts_pool == NULL) {
+		ssl_iostream_contexts_pool =
+			pool_alloconly_create(MEMPOOL_GROWING"ssl iostream context cache", 1024);
+		hash_table_create(&ssl_iostream_contexts,
+				  ssl_iostream_contexts_pool, 0,
+				  ssl_iostream_context_cache_hash,
+				  ssl_iostream_context_cache_cmp);
+	}
+	ssl_iostream_settings_drop_stream_only(&lookup.set);
+
+	ctx = hash_table_lookup(ssl_iostream_contexts, &lookup);
+	if (ctx != NULL) {
+		ssl_iostream_context_ref(ctx);
+		*ctx_r = ctx;
+		return 0;
+	}
+
+	/* add to cache */
+	if (server) {
+		if (ssl_iostream_context_init_server(&lookup.set, &ctx, error_r) < 0)
+			return -1;
+	} else {
+		if (ssl_iostream_context_init_client(&lookup.set, &ctx, error_r) < 0)
+			return -1;
+	}
+
+	cache = p_new(ssl_iostream_contexts_pool,
+		      struct ssl_iostream_context_cache, 1);
+	cache->server = server;
+	ssl_iostream_settings_init_from(ssl_iostream_contexts_pool,
+					&cache->set, &lookup.set);
+	hash_table_insert(ssl_iostream_contexts, cache, ctx);
+
+	ssl_iostream_context_ref(ctx);
+	*ctx_r = ctx;
+	return 0;
+}
+
+int ssl_iostream_client_context_cache_get(const struct ssl_iostream_settings *set,
+					  struct ssl_iostream_context **ctx_r,
+					  const char **error_r)
+{
+	return ssl_iostream_context_cache_get(set, FALSE, ctx_r, error_r);
+}
+
+int ssl_iostream_server_context_cache_get(const struct ssl_iostream_settings *set,
+					  struct ssl_iostream_context **ctx_r,
+					  const char **error_r)
+{
+	return ssl_iostream_context_cache_get(set, TRUE, ctx_r, error_r);
+}
+
+void ssl_iostream_context_cache_free(void)
+{
+	struct hash_iterate_context *iter;
+	struct ssl_iostream_context_cache *lookup;
+	struct ssl_iostream_context *ctx;
+
+	if (ssl_iostream_contexts_pool == NULL)
+		return;
+
+	iter = hash_table_iterate_init(ssl_iostream_contexts);
+	while (hash_table_iterate(iter, ssl_iostream_contexts, &lookup, &ctx))
+		ssl_iostream_context_unref(&ctx);
+	hash_table_iterate_deinit(&iter);
+	hash_table_destroy(&ssl_iostream_contexts);
+	pool_unref(&ssl_iostream_contexts_pool);
+}
diff --git a/src/lib-ssl-iostream/iostream-ssl-private.h b/src/lib-ssl-iostream/iostream-ssl-private.h
new file mode 100644
index 0000000..c0f4a3a
--- /dev/null
+++ b/src/lib-ssl-iostream/iostream-ssl-private.h
@@ -0,0 +1,64 @@
+#ifndef IOSTREAM_SSL_PRIVATE_H
+#define IOSTREAM_SSL_PRIVATE_H
+
+#include "iostream-ssl.h"
+
+struct iostream_ssl_vfuncs {
+	int (*global_init)(const struct ssl_iostream_settings *set,
+			   const char **error_r);
+	int (*context_init_client)(const struct ssl_iostream_settings *set,
+				   struct ssl_iostream_context **ctx_r,
+				   const char **error_r);
+	int (*context_init_server)(const struct ssl_iostream_settings *set,
+				   struct ssl_iostream_context **ctx_r,
+				   const char **error_r);
+	void (*context_ref)(struct ssl_iostream_context *ctx);
+	void (*context_unref)(struct ssl_iostream_context *ctx);
+
+	int (*create)(struct ssl_iostream_context *ctx, const char *host,
+		      const struct ssl_iostream_settings *set,
+		      struct istream **input, struct ostream **output,
+		      struct ssl_iostream **iostream_r, const char **error_r);
+	void (*unref)(struct ssl_iostream *ssl_io);
+	void (*destroy)(struct ssl_iostream *ssl_io);
+
+	int (*handshake)(struct ssl_iostream *ssl_io);
+	void (*set_handshake_callback)(struct ssl_iostream *ssl_io,
+				       ssl_iostream_handshake_callback_t *callback,
+				       void *context);
+	void (*set_sni_callback)(struct ssl_iostream *ssl_io,
+				 ssl_iostream_sni_callback_t *callback,
+				 void *context);
+	void (*change_context)(struct ssl_iostream *ssl_io,
+			       struct ssl_iostream_context *ctx);
+
+	void (*set_log_prefix)(struct ssl_iostream *ssl_io, const char *prefix);
+	bool (*is_handshaked)(const struct ssl_iostream *ssl_io);
+	bool (*has_handshake_failed)(const struct ssl_iostream *ssl_io);
+	bool (*has_valid_client_cert)(const struct ssl_iostream *ssl_io);
+	bool (*has_broken_client_cert)(struct ssl_iostream *ssl_io);
+	bool (*cert_match_name)(struct ssl_iostream *ssl_io, const char *name,
+				const char **reason_r);
+	const char *(*get_peer_name)(struct ssl_iostream *ssl_io);
+	const char *(*get_server_name)(struct ssl_iostream *ssl_io);
+	const char *(*get_compression)(struct ssl_iostream *ssl_io);
+	const char *(*get_security_string)(struct ssl_iostream *ssl_io);
+	const char *(*get_last_error)(struct ssl_iostream *ssl_io);
+	const char *(*get_cipher)(struct ssl_iostream *ssl_io, unsigned int *bits_r);
+	const char *(*get_pfs)(struct ssl_iostream *ssl_io);
+	const char *(*get_protocol_name)(struct ssl_iostream *ssl_io);
+};
+
+void iostream_ssl_module_init(const struct iostream_ssl_vfuncs *vfuncs);
+
+/* Returns TRUE if both settings are equal. Note that NULL and "" aren't
+   treated equal. */
+bool ssl_iostream_settings_equals(const struct ssl_iostream_settings *set1,
+				  const struct ssl_iostream_settings *set2);
+/* Clear out all stream-only settings, so only settings useful for a context
+   are left. */
+void ssl_iostream_settings_drop_stream_only(struct ssl_iostream_settings *set);
+
+void ssl_iostream_unref(struct ssl_iostream **ssl_io);
+
+#endif
diff --git a/src/lib-ssl-iostream/iostream-ssl-test.c b/src/lib-ssl-iostream/iostream-ssl-test.c
new file mode 100644
index 0000000..50d0aab
--- /dev/null
+++ b/src/lib-ssl-iostream/iostream-ssl-test.c
@@ -0,0 +1,158 @@
+/* Copyright (c) 2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+
+#include "iostream-ssl.h"
+#include "iostream-ssl-test.h"
+
+static const char *test_ca_cert =
+	"-----BEGIN CERTIFICATE-----\n"
+	"MIIF4TCCA8mgAwIBAgICEAAwDQYJKoZIhvcNAQELBQAwgYQxCzAJBgNVBAYTAk5M\n"
+	"MRMwEQYDVQQIDApHZWxkZXJsYW5kMRIwEAYDVQQHDAlCYXJuZXZlbGQxGjAYBgNV\n"
+	"BAoMEUNoaWNrZW4gQ29vcCBCLlYuMR4wHAYDVQQLDBVDZXJ0aWZpY2F0ZSBBdXRo\n"
+	"b3JpdHkxEDAOBgNVBAMMB1Jvb3QgQ0EwIBcNMTgwMjA4MjEyODE2WhgPMjExODAx\n"
+	"MTUyMTI4MTZaMHgxCzAJBgNVBAYTAk5MMRMwEQYDVQQIDApHZWxkZXJsYW5kMRow\n"
+	"GAYDVQQKDBFDaGlja2VuIENvb3AgQi5WLjEeMBwGA1UECwwVQ2VydGlmaWNhdGUg\n"
+	"QXV0aG9yaXR5MRgwFgYDVQQDDA9JbnRlcm1lZGlhdGUgQ0EwggIiMA0GCSqGSIb3\n"
+	"DQEBAQUAA4ICDwAwggIKAoICAQDgwuwUQ387ALkBO2YAvLiOi0rhQMis+TY34tpN\n"
+	"96Xx9Jaa8gdiAW9y3l8hGFm1+Ens5ZukwMysUoP7rrI5s0XOgCTChzrB4dEnbWHj\n"
+	"2YUYUBVLTLqZ4PTbY6xyrjYHKol1govkU+wclmyeI+Os946U0HFubg+KuXGZ2oLM\n"
+	"iYAmur/oxickEwJX932KhzQS4xdT5o38cVv470ot6eNEAiZcufP/gBSjAyUd8Wge\n"
+	"bwpW64fE/0LyCXYZrK5LWG1dMPC8MpETb8uLAB33r6q3yLTcEWg79bes7SgNrQdx\n"
+	"ncUXBoh8YSJvniZQ6OhwENPGTNhZWzgltDZHASyKXY2ojV70D8iiy/uB+owPSTla\n"
+	"txnu7z8B4kVCBWhCUizk7upjZNA0aFutjEHyYLtxqbTon+iLYm7M4iaga23YBdMU\n"
+	"1QVtulmUY6dcjTJ8GG3uo+qglPKuSodLSb23ovxAdVdIF+BNukd18ZhEIAe08hbw\n"
+	"YBHUYsKNkTMYcwxSgK3yQ4tQw0Cky4wAdsDv1XBK0LZ8+wnuWjnrnO/TRvgLWRU4\n"
+	"qI36OEMk9T0bxi+UwP3mzu78OoMCCdf67ccZ2/zFfHg+dqTBc9zV0sYJ/RQvmEN1\n"
+	"KDgqJAhz+VkDzTBiQYxoztTgBv9yxYufFvwZX4uhsvtMXUuRfvoVwK16vPXnMHwF\n"
+	"muIvwwIDAQABo2YwZDAdBgNVHQ4EFgQUWv/zcVnDWf53C2iN9f6uyUmhp1EwHwYD\n"
+	"VR0jBBgwFoAUsSOnSayEpzvbN21MEQGEyVKx+kIwEgYDVR0TAQH/BAgwBgEB/wIB\n"
+	"ADAOBgNVHQ8BAf8EBAMCAYYwDQYJKoZIhvcNAQELBQADggIBAJUlgJIHnnclDQMn\n"
+	"PSmruCl7bCRvLZYQtSiIv3/K4kPXJMYOvULoXGLA0+CdHoo06k8/TLk7gF1gNCPr\n"
+	"23z2+SCIuvVrVlveWyqD684yQ3UYeWoJnOv90F19267uELrWX4UMVE+z1r7iULyw\n"
+	"cxQokw6EGjw7xHiVETvNlHlmA0/8IuZv89CTztOP54NAXqu8WeloL/ipEhgj1HRx\n"
+	"TkuDf6SlTQ+mXKbiVJFiEA6rOsYFGGWE/SDNbLfx60OoHz0rQ95zw0rv/wPs1Oai\n"
+	"x71Ccuz/i2iI7ItXjQcUEcXvIDFJEMNXDaccIVmk1uda0Cm92W/sGc4vG2LUwEpl\n"
+	"LRj/x4Q39WaZTCrZzd6p2+6tYA45VnoblZ0enYU5XcQzryR/GC7VWFH1OvzOcSG5\n"
+	"NhpKIiWZvuMG5ilXyw7yh7cnWiPvGp8zCO7w1IOyk8sETQBstxuiALeEdrgdz6R5\n"
+	"jV5oIqsCmsIihfRgNufx/SImTJvue4uYgrKa4jo1tw+CFkEWPd7zXjferkxyU8C5\n"
+	"Y+Fr3yMuis5O4qa5mb94r0AQhc8MbCAuInSqNGX0Iu/UTg6Z+56omA2CnKGt6Rwd\n"
+	"LxLo2vhT9gTF88QwTMBPlhVjBbjTRhmY+mHv9gh3GczQ/i5VRXyYQH4h7EBtKFFI\n"
+	"t4mBWMavY+hS/zVkufYzUcUR7D1P\n"
+	"-----END CERTIFICATE-----\n"
+	"-----BEGIN CERTIFICATE-----\n"
+	"MIIF8jCCA9qgAwIBAgIJAN0zFa9E/xyxMA0GCSqGSIb3DQEBCwUAMIGEMQswCQYD\n"
+	"VQQGEwJOTDETMBEGA1UECAwKR2VsZGVybGFuZDESMBAGA1UEBwwJQmFybmV2ZWxk\n"
+	"MRowGAYDVQQKDBFDaGlja2VuIENvb3AgQi5WLjEeMBwGA1UECwwVQ2VydGlmaWNh\n"
+	"dGUgQXV0aG9yaXR5MRAwDgYDVQQDDAdSb290IENBMCAXDTE4MDIwODIxMjA1NloY\n"
+	"DzIyMTcxMjIyMjEyMDU2WjCBhDELMAkGA1UEBhMCTkwxEzARBgNVBAgMCkdlbGRl\n"
+	"cmxhbmQxEjAQBgNVBAcMCUJhcm5ldmVsZDEaMBgGA1UECgwRQ2hpY2tlbiBDb29w\n"
+	"IEIuVi4xHjAcBgNVBAsMFUNlcnRpZmljYXRlIEF1dGhvcml0eTEQMA4GA1UEAwwH\n"
+	"Um9vdCBDQTCCAiIwDQYJKoZIhvcNAQEBBQADggIPADCCAgoCggIBAKMvVLNtj1C+\n"
+	"ZQ4ypNIA5+zB8oseN65k8VqpyhcPAQv0M/HvOB8jXzWH4v1VfKOYkTxQXqu4v0RP\n"
+	"6k0awe/6FH0GDlYhKUuPNDH2djlGOVbq+qBdSXpC3UjEcksxIuigCmzdkuytnlhW\n"
+	"qQYnLVl6kXwYtzjWsetTZBGseCpSYBWnvdtG/MGQNozi03VsGFkj/fbwuLK7ZHVp\n"
+	"64QLk9j3IPZRPHUaFlnT+v2ySMjO8OncsZ/fMZ/nxmt8GJ/68cMy9czydauz2KZs\n"
+	"pQEFS6s/HCmRXT1VQZ7zw5V/PBnF7ecveTaQtxJoNO4Pr7sh77El/ChUxN1Acw4N\n"
+	"2UH/06k6xnirLsvJonCRbVX3bxPBoDzGHjPqb7r0AKD0WBvrzgjeooSjobEtcIvA\n"
+	"LntiGKp4KtvWKcANPWkutH9X71U7M773oMmrz5fWvz9yv3wVuyblZSaMBwrV16GX\n"
+	"mcym6KF+Oj7j86jNq4wxNtjiQVV0QZcBijtnWpHaD5EMhI/TZvLK9oCFyAL92Wzi\n"
+	"t95r8g3D/8ue0CHqB/EpodH88MdVwr7sgxLQ40KibpErOXb93CJnq/7MVMO/EzTj\n"
+	"4XiGGUOo0elLqEPjzBO6AiGEgXAE2iNoghX79cbMQFtk9sK7XdMVLoXwBvt+Naaz\n"
+	"w96+7R+rZ4SsfrtlrP7xoCPJXbeQ4YI9AgMBAAGjYzBhMB0GA1UdDgQWBBSxI6dJ\n"
+	"rISnO9s3bUwRAYTJUrH6QjAfBgNVHSMEGDAWgBSxI6dJrISnO9s3bUwRAYTJUrH6\n"
+	"QjAPBgNVHRMBAf8EBTADAQH/MA4GA1UdDwEB/wQEAwIBhjANBgkqhkiG9w0BAQsF\n"
+	"AAOCAgEAQ30mub/GBwThYX3h9p01kQh+/eXXQ47h1xG3B870EwJ2y36wlGbAhZmE\n"
+	"7o1kDZwhNMR4NxT2PSWQHn8m6RiuSGAG9DU2q55tPEZg2DqkQmoCFvV3n2MVIAwL\n"
+	"rZ8c9EaoM5RkeeDBmuVo8H1aCvd5oLJ5j64z6wkgsSRwVXkxQLOAEdmRSVHN/c/6\n"
+	"QEdg0Uh5wkeC7R5wiwQUEkhLie+XwUPG7dIJHWp9g5oVO7IN+KWBLWiqbAJhVFhF\n"
+	"evOSqGDRV/Q2kfwSqDRrokk7CaE8KO/i+AUTF4TFQc/ewCLSeBSkvV7ORXBbe7ob\n"
+	"ShGViL7WEngpGAVoDZEsSViXQ36a5zxCvYcGjHcsKUITPMiD55x0aKNWjc0XfEg4\n"
+	"JtWvYWwygxTcefbs9pxHrmEnyCPpyDB8cPj866JAeaEAhxhDtSqaBE/ek576aJ+Z\n"
+	"ZaGjBQDDhRndLhTPAx1EXB8jgl/yjD+KMUqHs39UowKH25iBxMiW3R1XDIyYFGyi\n"
+	"+UFP+5NgokW/z6JfpUYd4W3jRcareS10UrLQC8tk4vvixk+1MuNKmzBy2eRITYZz\n"
+	"KiYX6NTvbvRt6XsKil8ypHKvWH+i2Cn3JrnTaCzJ4y66lnbRs4/ZnRceqRz35i39\n"
+	"rNT5Ier3SjmyIulxnmoYXHInIcS0TSV1+byyaTUCHKHLx12RxAM=\n"
+	"-----END CERTIFICATE-----\n";
+
+static const char *test_server_cert =
+	"-----BEGIN CERTIFICATE-----\n"
+	"MIIF/jCCA+agAwIBAgICEAMwDQYJKoZIhvcNAQELBQAweDELMAkGA1UEBhMCTkwx\n"
+	"EzARBgNVBAgMCkdlbGRlcmxhbmQxGjAYBgNVBAoMEUNoaWNrZW4gQ29vcCBCLlYu\n"
+	"MR4wHAYDVQQLDBVDZXJ0aWZpY2F0ZSBBdXRob3JpdHkxGDAWBgNVBAMMD0ludGVy\n"
+	"bWVkaWF0ZSBDQTAgFw0xOTAyMTkxMDI2MzdaGA8yMTIxMTAyMjEwMjYzN1owgbUx\n"
+	"CzAJBgNVBAYTAk5MMRMwEQYDVQQIDApHZWxkZXJsYW5kMRIwEAYDVQQHDAlCYXJu\n"
+	"ZXZlbGQxGjAYBgNVBAoMEUNoaWNrZW4gQ29vcCBCLlYuMSIwIAYDVQQLDBlDaGlj\n"
+	"a2VuIENvb3AgV2ViIFNlcnZpY2VzMRIwEAYDVQQDDAkxMjcuMC4wLjExKTAnBgkq\n"
+	"hkiG9w0BCQEWGmhlbm5pZUBjaGlja2VuY29vcC5leGFtcGxlMIIBIjANBgkqhkiG\n"
+	"9w0BAQEFAAOCAQ8AMIIBCgKCAQEA3mNxJKdYUP88HHAPP8FWSDYKofxg2ECJsBQP\n"
+	"cIEvhuDsOpU+kBp3CbVFL+it4kNq7KvYvQyGvag8JA3RFrvsj3/nFM99lPm6RP1y\n"
+	"h9hNYVWRHHWKyOTdwqhk9bOrLk8j8fxw4NfQ/dkURYLJ0OtVTtJELJsxif5BfIAP\n"
+	"ypHayfnFoNa3rFG3uGULzJlb5JOHJHr7vxOTrRUZGYFZeBFacKF14CHYMUkpr9dv\n"
+	"BLaGqKFF0Lx2TU0tzRIXGu2AIFydcM0eGhCFLOV8YqxwT0R+XyNoNG9jRVSewWx0\n"
+	"r7rAF/93vARdRQVDmVoLmxrUMldYN7mQ9MsuGkMBfecLO4HqrQIDAQABo4IBUDCC\n"
+	"AUwwCQYDVR0TBAIwADARBglghkgBhvhCAQEEBAMCBkAwMwYJYIZIAYb4QgENBCYW\n"
+	"JE9wZW5TU0wgR2VuZXJhdGVkIFNlcnZlciBDZXJ0aWZpY2F0ZTAdBgNVHQ4EFgQU\n"
+	"Ez4hL16BDA+GMrQs+g3/1Do4Vr4wgbIGA1UdIwSBqjCBp4AUWv/zcVnDWf53C2iN\n"
+	"9f6uyUmhp1GhgYqkgYcwgYQxCzAJBgNVBAYTAk5MMRMwEQYDVQQIDApHZWxkZXJs\n"
+	"YW5kMRIwEAYDVQQHDAlCYXJuZXZlbGQxGjAYBgNVBAoMEUNoaWNrZW4gQ29vcCBC\n"
+	"LlYuMR4wHAYDVQQLDBVDZXJ0aWZpY2F0ZSBBdXRob3JpdHkxEDAOBgNVBAMMB1Jv\n"
+	"b3QgQ0GCAhAAMA4GA1UdDwEB/wQEAwIFoDATBgNVHSUEDDAKBggrBgEFBQcDATAN\n"
+	"BgkqhkiG9w0BAQsFAAOCAgEAVbs9RDJiVvGAW2cQv5OvghvMECF2Lh0pxsyOeywz\n"
+	"AQBBEaz85ZTRjtQjTWxpJwgwnIFEmfMEpuZoDoffCWDKUNkt24DD9TN8kriHplPK\n"
+	"5P3qZsnuV/E6CiYxBNpYhEle001XO+sU3yjAMeynPZWSZVz1JnjAdh1+opVd62O8\n"
+	"RX7twWdaSUBdsw7JJ2tdtTPeYkyRqDbfQWZSbA4/3VOwLuOs38zgy5ZqHy+YF/MM\n"
+	"48D1cOI0K1qpJE4qYLzcoULSnJ6C8KsS9LsspiLSDGdEvFY0DnCOa/POG6WiuEGk\n"
+	"JGRD+bDbEPZmNU0OLWjzM3vC2qxjF2PC8Q4chhkm4s4cAT7DMf+nnwqTPGK1U3N3\n"
+	"S5xhHrQ1GMHDhrqmKIrBOxdc8Hg7CwCU+C7TXxIPuQlbdStqMW/lVfbRNKsm/Hr6\n"
+	"smOC/hTxuned5DxRkDTCKNof3bZt8k9dqFLjqj14txmITq7MLhJLcsXgECWe7HmX\n"
+	"imxYJzLHjJU6QoDqGXHEMNrIBp46aIOcTjJP6tfosgAzplj+o00xdpMH9Q9hG602\n"
+	"lpgS9JfemZI68jPTZeGie9wXilPp4kE4qmlxhKSsjh3RVHo6ju7uKI5vCBkk15C6\n"
+	"lQMIGAmkRJ5vkcpUWnO6dKCSQdru/gKn3X4JVAHwm4178gqfRkofT28xAZ+vZoFj\n"
+	"L7M=\n"
+	"-----END CERTIFICATE-----\n";
+
+static const char *test_server_key =
+	"-----BEGIN RSA PRIVATE KEY-----\n"
+	"MIIEowIBAAKCAQEA3mNxJKdYUP88HHAPP8FWSDYKofxg2ECJsBQPcIEvhuDsOpU+\n"
+	"kBp3CbVFL+it4kNq7KvYvQyGvag8JA3RFrvsj3/nFM99lPm6RP1yh9hNYVWRHHWK\n"
+	"yOTdwqhk9bOrLk8j8fxw4NfQ/dkURYLJ0OtVTtJELJsxif5BfIAPypHayfnFoNa3\n"
+	"rFG3uGULzJlb5JOHJHr7vxOTrRUZGYFZeBFacKF14CHYMUkpr9dvBLaGqKFF0Lx2\n"
+	"TU0tzRIXGu2AIFydcM0eGhCFLOV8YqxwT0R+XyNoNG9jRVSewWx0r7rAF/93vARd\n"
+	"RQVDmVoLmxrUMldYN7mQ9MsuGkMBfecLO4HqrQIDAQABAoIBAQCGV4Az6ju5wlXn\n"
+	"v/IWS4751Fub+z/tox8KFTQ2fHPfgORzh1Dh8HrUjIKdLGxOcPeYvT8TBQwoagba\n"
+	"qNYUa7W+Aj/wHF/6rNlPb+POGGa2U+BzVrZeIZOtUdibbMwOD5ThS+RMj1Ma5hYO\n"
+	"37FW2bMRCIhSgfXtLIEW2q2va2jF9VI+c7F9dL01COG65nwUSJaRSLPrK5WbVNZE\n"
+	"yNm2st88iiu3TtPJGty+wmFgyV0PjAYYqxVEPs6qcmYMuHrfKlrntDfYai6x7fb+\n"
+	"RDfHhmqmn2oV/LGl7YtH+jBML9WG+Rfw+M7pYsd3ffRjG4aRxSTotu0QZfjduP0a\n"
+	"NZL1C3OBAoGBAPrzC4X2/fPGfyHksg+ecPS2Pvnyr+L9Gtg2Dg9wAONbmYqGKYxa\n"
+	"7DUBr6WWbOy9qJKk1CHR2Gn5FK3KbHG1PhLiOuG00kjm6imSCFTpJ3sBXUCl9qMk\n"
+	"FJnBifT4//INLFIcLjFlygR20hHgqyLU8P2kKzM+7iPaF1GYdILYHnExAoGBAOLd\n"
+	"PmKFcwuD4VfzTwK/Va0L8FFi3Oo7O4OE+9PyfTCJ8fH9PW03e4DiddjM0djDovWW\n"
+	"sm1ySVTfHjE0rsnaMGngPvqhG5T6IMUtFowEa2VwqwfFrPzK4PUYeRV1G+rTL1ZX\n"
+	"RGV1nPxCRXog91gzDCuyYB7jblrjG+DP+ZfGI5I9AoGAJc8Mg2iNJndXnDGqqjPC\n"
+	"7PuwTVRFL7vWmZC7WZQUbizU20wPYngocmwInLgnPRvuE/oFg/rr0juW5ABFinQ2\n"
+	"H/45xNvLevRff1fjLXfbXOr9s8nNeRLsj6XbNS920G8vqEdaplKhtz53s/3Xiu3u\n"
+	"SSi84YGvu3MWZFLF6xjIrWECgYAI2tXahpbs9iLPigGle85eSL8CjjdNNS6nfYNO\n"
+	"zIIyaM/2wAmrv6SkbTJoWeY+7bPong8s0m8mTucgyIuh+VA2cbhDlBI9iF3LFG1y\n"
+	"3aFLflBOp1qPK2QIbQIc4ktKqR+J4TIcO7D676NClxLQcH2jHv09d2cRSRgHeFan\n"
+	"o+YziQKBgEtqnknKgedinexHheBhE/fo49bHwNYZBfA5ZKqQDguNBafU1BUOmPEO\n"
+	"eNb8S5cJDMR7zKeZJ9dHzf4j78sITigwxt8+Ee6VY92U/uTFkPKZNLpAr3OfDSdh\n"
+	"z+M/zgztKqdrSKhr64g/3Dbbe+XqdeGe8MIx+P+QN+SrJNNaNZ1r\n"
+	"-----END RSA PRIVATE KEY-----\n";
+
+void ssl_iostream_test_settings_server(struct ssl_iostream_settings *test_set)
+{
+	i_zero(test_set);
+	test_set->ca = test_ca_cert;
+	test_set->cert.cert = test_server_cert;
+	test_set->cert.key = test_server_key;
+	test_set->skip_crl_check = TRUE;
+}
+
+void ssl_iostream_test_settings_client(struct ssl_iostream_settings *test_set)
+{
+	i_zero(test_set);
+	test_set->ca = test_ca_cert;
+	test_set->skip_crl_check = TRUE;
+}
diff --git a/src/lib-ssl-iostream/iostream-ssl-test.h b/src/lib-ssl-iostream/iostream-ssl-test.h
new file mode 100644
index 0000000..82c5811
--- /dev/null
+++ b/src/lib-ssl-iostream/iostream-ssl-test.h
@@ -0,0 +1,9 @@
+#ifndef IOSTREAM_SSL_TEST_H
+#define IOSTREAM_SSL_TEST_H
+
+struct ssl_iostream_settings;
+
+void ssl_iostream_test_settings_server(struct ssl_iostream_settings *test_set);
+void ssl_iostream_test_settings_client(struct ssl_iostream_settings *test_set);
+
+#endif
diff --git a/src/lib-ssl-iostream/iostream-ssl.c b/src/lib-ssl-iostream/iostream-ssl.c
new file mode 100644
index 0000000..430e69d
--- /dev/null
+++ b/src/lib-ssl-iostream/iostream-ssl.c
@@ -0,0 +1,351 @@
+/* Copyright (c) 2009-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "module-dir.h"
+#include "iostream-ssl-private.h"
+
+#define OFFSET(name) offsetof(struct ssl_iostream_settings, name)
+static const size_t ssl_iostream_settings_string_offsets[] = {
+	OFFSET(min_protocol),
+	OFFSET(cipher_list),
+	OFFSET(ciphersuites),
+	OFFSET(curve_list),
+	OFFSET(ca),
+	OFFSET(ca_file),
+	OFFSET(ca_dir),
+	OFFSET(cert.cert),
+	OFFSET(cert.key),
+	OFFSET(cert.key_password),
+	OFFSET(alt_cert.cert),
+	OFFSET(alt_cert.key),
+	OFFSET(alt_cert.key_password),
+	OFFSET(dh),
+	OFFSET(cert_username_field),
+	OFFSET(crypto_device),
+};
+
+static bool ssl_module_loaded = FALSE;
+#ifdef HAVE_SSL
+static struct module *ssl_module = NULL;
+#endif
+static const struct iostream_ssl_vfuncs *ssl_vfuncs = NULL;
+
+#ifdef HAVE_SSL
+static void ssl_module_unload(void)
+{
+	ssl_iostream_context_cache_free();
+	module_dir_unload(&ssl_module);
+}
+#endif
+
+void iostream_ssl_module_init(const struct iostream_ssl_vfuncs *vfuncs)
+{
+	ssl_vfuncs = vfuncs;
+	ssl_module_loaded = TRUE;
+}
+
+int ssl_module_load(const char **error_r)
+{
+#ifdef HAVE_SSL
+	const char *plugin_name = "ssl_iostream_openssl";
+	struct module_dir_load_settings mod_set;
+
+	i_zero(&mod_set);
+	mod_set.abi_version = DOVECOT_ABI_VERSION;
+	mod_set.setting_name = "<built-in lib-ssl-iostream lookup>";
+	mod_set.require_init_funcs = TRUE;
+	ssl_module = module_dir_load(MODULE_DIR, plugin_name, &mod_set);
+	if (module_dir_try_load_missing(&ssl_module, MODULE_DIR, plugin_name,
+					&mod_set, error_r) < 0)
+		return -1;
+	module_dir_init(ssl_module);
+	if (!ssl_module_loaded) {
+		*error_r = t_strdup_printf(
+			"%s didn't call iostream_ssl_module_init() - SSL not initialized",
+			plugin_name);
+		module_dir_unload(&ssl_module);
+		return -1;
+	}
+
+	/* Destroy SSL module after (most of) the others. Especially lib-fs
+	   backends may still want to access SSL module in their own
+	   atexit-callbacks. */
+	lib_atexit_priority(ssl_module_unload, LIB_ATEXIT_PRIORITY_LOW);
+	return 0;
+#else
+	*error_r = "SSL support not compiled in";
+	return -1;
+#endif
+}
+
+int io_stream_ssl_global_init(const struct ssl_iostream_settings *set,
+			      const char **error_r)
+{
+	return ssl_vfuncs->global_init(set, error_r);
+}
+
+int ssl_iostream_context_init_client(const struct ssl_iostream_settings *set,
+				     struct ssl_iostream_context **ctx_r,
+				     const char **error_r)
+{
+	struct ssl_iostream_settings set_copy = *set;
+
+	/* ensure this is set to TRUE */
+	set_copy.verify_remote_cert = TRUE;
+
+	if (!ssl_module_loaded) {
+		if (ssl_module_load(error_r) < 0)
+			return -1;
+	}
+	if (io_stream_ssl_global_init(&set_copy, error_r) < 0)
+		return -1;
+	return ssl_vfuncs->context_init_client(&set_copy, ctx_r, error_r);
+}
+
+int ssl_iostream_context_init_server(const struct ssl_iostream_settings *set,
+				     struct ssl_iostream_context **ctx_r,
+				     const char **error_r)
+{
+	if (!ssl_module_loaded) {
+		if (ssl_module_load(error_r) < 0)
+			return -1;
+	}
+	if (io_stream_ssl_global_init(set, error_r) < 0)
+		return -1;
+	return ssl_vfuncs->context_init_server(set, ctx_r, error_r);
+}
+
+void ssl_iostream_context_ref(struct ssl_iostream_context *ctx)
+{
+	ssl_vfuncs->context_ref(ctx);
+}
+
+void ssl_iostream_context_unref(struct ssl_iostream_context **_ctx)
+{
+	struct ssl_iostream_context *ctx = *_ctx;
+
+	if (*_ctx == NULL)
+		return;
+	*_ctx = NULL;
+	ssl_vfuncs->context_unref(ctx);
+}
+
+int io_stream_create_ssl_client(struct ssl_iostream_context *ctx, const char *host,
+				const struct ssl_iostream_settings *set,
+				struct istream **input, struct ostream **output,
+				struct ssl_iostream **iostream_r,
+				const char **error_r)
+{
+	struct ssl_iostream_settings set_copy = *set;
+	set_copy.verify_remote_cert = TRUE;
+	return ssl_vfuncs->create(ctx, host, &set_copy, input, output,
+				  iostream_r, error_r);
+}
+
+int io_stream_create_ssl_server(struct ssl_iostream_context *ctx,
+				const struct ssl_iostream_settings *set,
+				struct istream **input, struct ostream **output,
+				struct ssl_iostream **iostream_r,
+				const char **error_r)
+{
+	return ssl_vfuncs->create(ctx, NULL, set, input, output,
+				  iostream_r, error_r);
+}
+
+void ssl_iostream_unref(struct ssl_iostream **_ssl_io)
+{
+	struct ssl_iostream *ssl_io = *_ssl_io;
+
+	*_ssl_io = NULL;
+	ssl_vfuncs->unref(ssl_io);
+}
+
+void ssl_iostream_destroy(struct ssl_iostream **_ssl_io)
+{
+	struct ssl_iostream *ssl_io;
+
+	if (_ssl_io == NULL || *_ssl_io == NULL)
+		return;
+
+	ssl_io = *_ssl_io;
+	*_ssl_io = NULL;
+	ssl_vfuncs->destroy(ssl_io);
+}
+
+void ssl_iostream_set_log_prefix(struct ssl_iostream *ssl_io,
+				 const char *prefix)
+{
+	ssl_vfuncs->set_log_prefix(ssl_io, prefix);
+}
+
+int ssl_iostream_handshake(struct ssl_iostream *ssl_io)
+{
+	return ssl_vfuncs->handshake(ssl_io);
+}
+
+void ssl_iostream_set_handshake_callback(struct ssl_iostream *ssl_io,
+					 ssl_iostream_handshake_callback_t *callback,
+					 void *context)
+{
+	ssl_vfuncs->set_handshake_callback(ssl_io, callback, context);
+}
+
+void ssl_iostream_set_sni_callback(struct ssl_iostream *ssl_io,
+				   ssl_iostream_sni_callback_t *callback,
+				   void *context)
+{
+	ssl_vfuncs->set_sni_callback(ssl_io, callback, context);
+}
+
+void ssl_iostream_change_context(struct ssl_iostream *ssl_io,
+				 struct ssl_iostream_context *ctx)
+{
+	ssl_vfuncs->change_context(ssl_io, ctx);
+}
+
+bool ssl_iostream_is_handshaked(const struct ssl_iostream *ssl_io)
+{
+	return ssl_vfuncs->is_handshaked(ssl_io);
+}
+
+bool ssl_iostream_has_handshake_failed(const struct ssl_iostream *ssl_io)
+{
+	return ssl_vfuncs->has_handshake_failed(ssl_io);
+}
+
+bool ssl_iostream_has_valid_client_cert(const struct ssl_iostream *ssl_io)
+{
+	return ssl_vfuncs->has_valid_client_cert(ssl_io);
+}
+
+bool ssl_iostream_has_broken_client_cert(struct ssl_iostream *ssl_io)
+{
+	return ssl_vfuncs->has_broken_client_cert(ssl_io);
+}
+
+bool ssl_iostream_cert_match_name(struct ssl_iostream *ssl_io, const char *name,
+				  const char **reason_r)
+{
+	return ssl_vfuncs->cert_match_name(ssl_io, name, reason_r);
+}
+
+int ssl_iostream_check_cert_validity(struct ssl_iostream *ssl_io,
+				     const char *host, const char **error_r)
+{
+	const char *reason;
+
+	if (!ssl_iostream_has_valid_client_cert(ssl_io)) {
+		if (!ssl_iostream_has_broken_client_cert(ssl_io))
+			*error_r = "SSL certificate not received";
+		else {
+			*error_r = t_strdup(ssl_iostream_get_last_error(ssl_io));
+			if (*error_r == NULL)
+				*error_r = "Received invalid SSL certificate";
+		}
+		return -1;
+	} else if (!ssl_iostream_cert_match_name(ssl_io, host, &reason)) {
+		*error_r = t_strdup_printf(
+			"SSL certificate doesn't match expected host name %s: %s",
+			host, reason);
+		return -1;
+	}
+	return 0;
+}
+
+const char *ssl_iostream_get_peer_name(struct ssl_iostream *ssl_io)
+{
+	return ssl_vfuncs->get_peer_name(ssl_io);
+}
+
+const char *ssl_iostream_get_server_name(struct ssl_iostream *ssl_io)
+{
+	return ssl_vfuncs->get_server_name(ssl_io);
+}
+
+const char *ssl_iostream_get_compression(struct ssl_iostream *ssl_io)
+{
+	return ssl_vfuncs->get_compression(ssl_io);
+}
+
+const char *ssl_iostream_get_security_string(struct ssl_iostream *ssl_io)
+{
+	return ssl_vfuncs->get_security_string(ssl_io);
+}
+
+const char *ssl_iostream_get_last_error(struct ssl_iostream *ssl_io)
+{
+	return ssl_vfuncs->get_last_error(ssl_io);
+}
+
+struct ssl_iostream_settings *ssl_iostream_settings_dup(pool_t pool,
+			const struct ssl_iostream_settings *old_set)
+{
+	struct ssl_iostream_settings *new_set;
+
+	new_set = p_new(pool, struct ssl_iostream_settings, 1);
+	ssl_iostream_settings_init_from(pool, new_set, old_set);
+	return new_set;
+}
+
+void ssl_iostream_settings_init_from(pool_t pool,
+				     struct ssl_iostream_settings *dest,
+				     const struct ssl_iostream_settings *src)
+{
+	unsigned int i;
+
+	*dest = *src;
+	for (i = 0; i < N_ELEMENTS(ssl_iostream_settings_string_offsets); i++) {
+		const size_t offset = ssl_iostream_settings_string_offsets[i];
+		const char *const *src_str = CONST_PTR_OFFSET(src, offset);
+		const char **dest_str = PTR_OFFSET(dest, offset);
+		*dest_str = p_strdup(pool, *src_str);
+	}
+}
+
+bool ssl_iostream_settings_equals(const struct ssl_iostream_settings *set1,
+				  const struct ssl_iostream_settings *set2)
+{
+	struct ssl_iostream_settings set1_nonstr, set2_nonstr;
+	unsigned int i;
+
+	set1_nonstr = *set1;
+	set2_nonstr = *set2;
+	for (i = 0; i < N_ELEMENTS(ssl_iostream_settings_string_offsets); i++) {
+		const size_t offset = ssl_iostream_settings_string_offsets[i];
+		const char **str1 = PTR_OFFSET(&set1_nonstr, offset);
+		const char **str2 = PTR_OFFSET(&set2_nonstr, offset);
+
+		if (null_strcmp(*str1, *str2) != 0)
+			return FALSE;
+
+		/* clear away the string pointer from the settings struct */
+		*str1 = NULL;
+		*str2 = NULL;
+	}
+	/* The set*_nonstr no longer have any pointers, so we can compare them
+	   directly. */
+	return memcmp(&set1_nonstr, &set2_nonstr, sizeof(set1_nonstr)) == 0;
+}
+
+void ssl_iostream_settings_drop_stream_only(struct ssl_iostream_settings *set)
+{
+	set->verbose = FALSE;
+	set->verbose_invalid_cert = FALSE;
+	set->allow_invalid_cert = FALSE;
+}
+
+const char *ssl_iostream_get_cipher(struct ssl_iostream *ssl_io,
+				    unsigned int *bits_r)
+{
+	return ssl_vfuncs->get_cipher(ssl_io, bits_r);
+}
+
+const char *ssl_iostream_get_pfs(struct ssl_iostream *ssl_io)
+{
+	return ssl_vfuncs->get_pfs(ssl_io);
+}
+
+const char *ssl_iostream_get_protocol_name(struct ssl_iostream *ssl_io)
+{
+	return ssl_vfuncs->get_protocol_name(ssl_io);
+}
diff --git a/src/lib-ssl-iostream/iostream-ssl.h b/src/lib-ssl-iostream/iostream-ssl.h
new file mode 100644
index 0000000..3224486
--- /dev/null
+++ b/src/lib-ssl-iostream/iostream-ssl.h
@@ -0,0 +1,175 @@
+#ifndef IOSTREAM_SSL_H
+#define IOSTREAM_SSL_H
+
+struct ssl_iostream;
+struct ssl_iostream_context;
+
+struct ssl_iostream_cert {
+	const char *cert;
+	const char *key;
+	const char *key_password;
+};
+
+struct ssl_iostream_settings {
+	/* NOTE: when updating, remember to update:
+	   ssl_iostream_settings_string_offsets[],
+	   ssl_iostream_settings_drop_stream_only() */
+	const char *min_protocol; /* both */
+	const char *cipher_list; /* both */
+	const char *ciphersuites; /* both, TLSv1.3 only */
+	const char *curve_list; /* both */
+	const char *ca, *ca_file, *ca_dir; /* context-only */
+	/* alternative cert is for providing certificate using
+	   different key algorithm */
+	struct ssl_iostream_cert cert; /* both */
+	struct ssl_iostream_cert alt_cert; /* both */
+	const char *dh; /* context-only */
+	const char *cert_username_field; /* both */
+	const char *crypto_device; /* context-only */
+
+	bool verbose, verbose_invalid_cert; /* stream-only */
+	bool skip_crl_check; /* context-only */
+	bool verify_remote_cert; /* neither/both */
+	bool allow_invalid_cert; /* stream-only */
+	bool prefer_server_ciphers; /* both */
+	bool compression; /* context-only */
+	bool tickets; /* context-only */
+};
+
+/* Load SSL module */
+int ssl_module_load(const char **error_r);
+
+/* Returns 0 if ok, -1 and sets error_r if failed. The returned error string
+   becomes available via ssl_iostream_get_last_error(). The callback most
+   likely should be calling ssl_iostream_check_cert_validity(). */
+typedef int
+ssl_iostream_handshake_callback_t(const char **error_r, void *context);
+/* Called when TLS SNI becomes available. */
+typedef int ssl_iostream_sni_callback_t(const char *name, const char **error_r,
+					void *context);
+
+/* Explicitly initialize SSL library globally. This is also done automatically
+   when the first SSL connection is created, but it may be useful to call it
+   earlier in case of chrooting. After the initialization is successful, any
+   further calls will just be ignored. Returns 0 on success, -1 on error. */
+int io_stream_ssl_global_init(const struct ssl_iostream_settings *set,
+			      const char **error_r);
+
+int io_stream_create_ssl_client(struct ssl_iostream_context *ctx, const char *host,
+				const struct ssl_iostream_settings *set,
+				struct istream **input, struct ostream **output,
+				struct ssl_iostream **iostream_r,
+				const char **error_r);
+int io_stream_create_ssl_server(struct ssl_iostream_context *ctx,
+				const struct ssl_iostream_settings *set,
+				struct istream **input, struct ostream **output,
+				struct ssl_iostream **iostream_r,
+				const char **error_r);
+/* Shutdown SSL connection and unreference ssl iostream.
+   The returned input and output streams must also be unreferenced. */
+void ssl_iostream_destroy(struct ssl_iostream **ssl_io);
+
+/* If verbose logging is enabled, use the specified log prefix */
+void ssl_iostream_set_log_prefix(struct ssl_iostream *ssl_io,
+				 const char *prefix);
+
+int ssl_iostream_handshake(struct ssl_iostream *ssl_io);
+/* Call the given callback when SSL handshake finishes. The callback must
+   verify whether the certificate and its hostname is valid. If there is no
+   callback, the default is to use ssl_iostream_check_cert_validity() with the
+   same host as given to io_stream_create_ssl_client()
+
+   Before the callback is called, certificate is only checked for issuer
+   and validity period. You should call ssl_iostream_check_cert_validity()
+   in your callback.
+*/
+void ssl_iostream_set_handshake_callback(struct ssl_iostream *ssl_io,
+					 ssl_iostream_handshake_callback_t *callback,
+					 void *context);
+/* Call the given callback when client sends SNI. The callback can change the
+   ssl_iostream's context (with different certificates) by using
+   ssl_iostream_change_context(). */
+void ssl_iostream_set_sni_callback(struct ssl_iostream *ssl_io,
+				   ssl_iostream_sni_callback_t *callback,
+				   void *context);
+void ssl_iostream_change_context(struct ssl_iostream *ssl_io,
+				 struct ssl_iostream_context *ctx);
+
+bool ssl_iostream_is_handshaked(const struct ssl_iostream *ssl_io);
+/* Returns TRUE if the remote cert is invalid, or handshake callback returned
+   failure. */
+bool ssl_iostream_has_handshake_failed(const struct ssl_iostream *ssl_io);
+bool ssl_iostream_has_valid_client_cert(const struct ssl_iostream *ssl_io);
+bool ssl_iostream_has_broken_client_cert(struct ssl_iostream *ssl_io);
+/* Checks certificate validity based, also performs name checking. Called by
+   default in handshake, unless handshake callback is set with
+   ssl_iostream_check_cert_validity().
+
+   Host should be set as the name you want to validate the certificate name(s)
+   against. Usually this is the host name you connected to.
+
+   This function is same as calling ssl_iostream_has_valid_client_cert()
+   and ssl_iostream_cert_match_name().
+ */
+int ssl_iostream_check_cert_validity(struct ssl_iostream *ssl_io,
+				     const char *host, const char **error_r);
+/* Returns TRUE if the given name matches the SSL stream's certificate.
+   The returned reason is a human-readable string explaining what exactly
+   matched the name, or why nothing matched. Note that this function works
+   only if the certificate was valid - using it when certificate is invalid
+   will always return FALSE before even checking the hostname. */
+bool ssl_iostream_cert_match_name(struct ssl_iostream *ssl_io, const char *name,
+				  const char **reason_r);
+const char *ssl_iostream_get_peer_name(struct ssl_iostream *ssl_io);
+const char *ssl_iostream_get_compression(struct ssl_iostream *ssl_io);
+const char *ssl_iostream_get_server_name(struct ssl_iostream *ssl_io);
+const char *ssl_iostream_get_security_string(struct ssl_iostream *ssl_io);
+/* Returns SSL context's current used cipher algorithm. Returns NULL
+   if SSL handshake has not been performed.
+
+   This returns values like 'AESGCM'
+*/
+const char *ssl_iostream_get_cipher(struct ssl_iostream *ssl_io,
+				    unsigned int *bits_r);
+/* Returns currently used forward secrecy algorithm, if available.
+   Returns NULL if handshake not done yet, empty string if missing.
+
+   This returns values like 'DH', 'ECDH' etc..
+*/
+const char *ssl_iostream_get_pfs(struct ssl_iostream *ssl_io);
+/* Returns currently used SSL protocol name. Returns NULL if handshake
+   has not yet been made.
+
+   This returns values like SSLv3, TLSv1, TLSv1.1, TLSv1.2
+*/
+const char *ssl_iostream_get_protocol_name(struct ssl_iostream *ssl_io);
+
+const char *ssl_iostream_get_last_error(struct ssl_iostream *ssl_io);
+
+int ssl_iostream_context_init_client(const struct ssl_iostream_settings *set,
+				     struct ssl_iostream_context **ctx_r,
+				     const char **error_r);
+int ssl_iostream_context_init_server(const struct ssl_iostream_settings *set,
+				     struct ssl_iostream_context **ctx_r,
+				     const char **error_r);
+void ssl_iostream_context_ref(struct ssl_iostream_context *ctx);
+void ssl_iostream_context_unref(struct ssl_iostream_context **ctx);
+
+struct ssl_iostream_settings *ssl_iostream_settings_dup(pool_t pool,
+			const struct ssl_iostream_settings *old_set);
+void ssl_iostream_settings_init_from(pool_t pool,
+				     struct ssl_iostream_settings *dest,
+				     const struct ssl_iostream_settings *src);
+
+/* Persistent cache of ssl_iostream_contexts. The context is permanently stored
+   until ssl_iostream_context_cache_free() is called. The returned context
+   must be unreferenced by the caller. */
+int ssl_iostream_client_context_cache_get(const struct ssl_iostream_settings *set,
+					  struct ssl_iostream_context **ctx_r,
+					  const char **error_r);
+int ssl_iostream_server_context_cache_get(const struct ssl_iostream_settings *set,
+					  struct ssl_iostream_context **ctx_r,
+					  const char **error_r);
+void ssl_iostream_context_cache_free(void);
+
+#endif
diff --git a/src/lib-ssl-iostream/istream-openssl.c b/src/lib-ssl-iostream/istream-openssl.c
new file mode 100644
index 0000000..f0446d9
--- /dev/null
+++ b/src/lib-ssl-iostream/istream-openssl.c
@@ -0,0 +1,130 @@
+/* Copyright (c) 2009-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "istream-private.h"
+#include "iostream-openssl.h"
+
+struct ssl_istream {
+	struct istream_private istream;
+	struct ssl_iostream *ssl_io;
+	bool seen_eof;
+};
+
+static void i_stream_ssl_close(struct iostream_private *stream,
+			       bool close_parent)
+{
+	struct ssl_istream *sstream = (struct ssl_istream *)stream;
+
+	if (close_parent)
+		i_stream_close(sstream->ssl_io->plain_input);
+}
+
+static void i_stream_ssl_destroy(struct iostream_private *stream)
+{
+	struct ssl_istream *sstream = (struct ssl_istream *)stream;
+
+	openssl_iostream_shutdown(sstream->ssl_io);
+	i_stream_free_buffer(&sstream->istream);
+	sstream->ssl_io->ssl_input = NULL;
+	ssl_iostream_unref(&sstream->ssl_io);
+}
+
+static ssize_t i_stream_ssl_read(struct istream_private *stream)
+{
+	struct ssl_istream *sstream = (struct ssl_istream *)stream;
+	struct ssl_iostream *ssl_io = sstream->ssl_io;
+	size_t size;
+	ssize_t ret, total_ret;
+
+	if (sstream->seen_eof) {
+		stream->istream.eof = TRUE;
+		return -1;
+	}
+
+	if (!ssl_io->handshaked) {
+		if ((ret = ssl_iostream_handshake(ssl_io)) <= 0) {
+			if (ret < 0) {
+				/* handshake failed */
+				i_assert(errno != 0);
+				io_stream_set_error(&stream->iostream,
+						    "%s", ssl_io->last_error);
+				stream->istream.stream_errno = errno;
+			}
+			return ret;
+		}
+	}
+	if (openssl_iostream_bio_sync(ssl_io,
+			OPENSSL_IOSTREAM_SYNC_TYPE_HANDSHAKE) < 0) {
+		i_assert(ssl_io->plain_stream_errno != 0 &&
+			 ssl_io->plain_stream_errstr != NULL);
+		io_stream_set_error(&stream->iostream,
+				    "%s", ssl_io->plain_stream_errstr);
+		stream->istream.stream_errno = ssl_io->plain_stream_errno;
+		return -1;
+	}
+
+	total_ret = 0;
+	for (;;) {
+		int pending = SSL_pending(ssl_io->ssl);
+
+		/* Allocate buffer space if needed. */
+		i_assert(stream->buffer_size >= stream->pos);
+		size = stream->buffer_size - stream->pos;
+		if ((pending > 0 || size == 0) &&
+		    !i_stream_try_alloc(stream, I_MAX(pending, 1), &size)) {
+			if (total_ret > 0)
+				break;
+			return -2;
+		}
+
+		ret = SSL_read(ssl_io->ssl, stream->w_buffer + stream->pos, size);
+		if (ret <= 0) {
+			/* failed to read anything */
+			ret = openssl_iostream_handle_error(ssl_io, ret,
+				(total_ret == 0 ?
+				 OPENSSL_IOSTREAM_SYNC_TYPE_CONTINUE_READ :
+				 OPENSSL_IOSTREAM_SYNC_TYPE_NONE), "SSL_read");
+			if (ret <= 0) {
+				if (ret == 0)
+					break;
+				if (ssl_io->last_error != NULL) {
+					io_stream_set_error(&stream->iostream,
+							    "%s", ssl_io->last_error);
+				}
+				if (errno != EPIPE)
+					stream->istream.stream_errno = errno;
+				stream->istream.eof = TRUE;
+				sstream->seen_eof = TRUE;
+				if (total_ret > 0)
+					break;
+				return -1;
+			}
+			/* we did some BIO I/O, try reading again */
+			continue;
+		}
+		stream->pos += ret;
+		total_ret += ret;
+	}
+	if (SSL_pending(ssl_io->ssl) > 0)
+		i_stream_set_input_pending(ssl_io->ssl_input, TRUE);
+	return total_ret;
+}
+
+struct istream *openssl_i_stream_create_ssl(struct ssl_iostream *ssl_io)
+{
+	struct ssl_istream *sstream;
+
+	ssl_io->refcount++;
+
+	sstream = i_new(struct ssl_istream, 1);
+	sstream->ssl_io = ssl_io;
+	sstream->istream.iostream.close = i_stream_ssl_close;
+	sstream->istream.iostream.destroy = i_stream_ssl_destroy;
+	sstream->istream.max_buffer_size =
+		ssl_io->plain_input->real_stream->max_buffer_size;
+	sstream->istream.read = i_stream_ssl_read;
+
+	sstream->istream.istream.readable_fd = FALSE;
+	return i_stream_create(&sstream->istream, NULL,
+			       i_stream_get_fd(ssl_io->plain_input), 0);
+}
diff --git a/src/lib-ssl-iostream/ostream-openssl.c b/src/lib-ssl-iostream/ostream-openssl.c
new file mode 100644
index 0000000..8434a9b
--- /dev/null
+++ b/src/lib-ssl-iostream/ostream-openssl.c
@@ -0,0 +1,339 @@
+/* Copyright (c) 2009-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "buffer.h"
+#include "istream.h"
+#include "ostream-private.h"
+#include "iostream-openssl.h"
+
+struct ssl_ostream {
+	struct ostream_private ostream;
+	struct ssl_iostream *ssl_io;
+	buffer_t *buffer;
+
+	bool shutdown:1;
+};
+
+static void
+o_stream_ssl_close(struct iostream_private *stream, bool close_parent)
+{
+	struct ssl_ostream *sstream = (struct ssl_ostream *)stream;
+
+	if (close_parent)
+		o_stream_close(sstream->ssl_io->plain_output);
+}
+
+static void o_stream_ssl_destroy(struct iostream_private *stream)
+{
+	struct ssl_ostream *sstream = (struct ssl_ostream *)stream;
+	struct istream *ssl_input = sstream->ssl_io->ssl_input;
+
+	openssl_iostream_shutdown(sstream->ssl_io);
+	sstream->ssl_io->ssl_output = NULL;
+	i_stream_unref(&ssl_input);
+	ssl_iostream_unref(&sstream->ssl_io);
+	buffer_free(&sstream->buffer);
+}
+
+static size_t get_buffer_avail_size(const struct ssl_ostream *sstream)
+{
+	if (sstream->ostream.max_buffer_size == 0) {
+		if (sstream->buffer == NULL)
+			return 0;
+		/* we're requested to use whatever space is available in
+		   the buffer */
+		return buffer_get_writable_size(sstream->buffer) - sstream->buffer->used;
+	} else {
+		size_t buffer_used = (sstream->buffer == NULL ? 0 :
+				      sstream->buffer->used);
+		return sstream->ostream.max_buffer_size > buffer_used ?
+			sstream->ostream.max_buffer_size - buffer_used : 0;
+	}
+}
+
+static size_t
+o_stream_ssl_buffer(struct ssl_ostream *sstream, const struct const_iovec *iov,
+		    unsigned int iov_count, size_t bytes_sent)
+{
+	size_t avail, skip_left, size;
+	unsigned int i;
+
+	if (sstream->buffer == NULL)
+		sstream->buffer = buffer_create_dynamic(default_pool,
+			I_MIN(IO_BLOCK_SIZE, sstream->ostream.max_buffer_size));
+
+	skip_left = bytes_sent;
+	for (i = 0; i < iov_count; i++) {
+		if (skip_left < iov[i].iov_len)
+			break;
+		skip_left -= iov[i].iov_len;
+	}
+
+	avail = get_buffer_avail_size(sstream);
+	if (i < iov_count && skip_left > 0) {
+		size = I_MIN(iov[i].iov_len - skip_left, avail);
+		buffer_append(sstream->buffer,
+			      CONST_PTR_OFFSET(iov[i].iov_base, skip_left),
+			      size);
+		bytes_sent += size;
+		avail -= size;
+		if (size != iov[i].iov_len)
+			i = iov_count;
+	}
+	if (avail > 0)
+		o_stream_set_flush_pending(sstream->ssl_io->plain_output, TRUE);
+
+	for (; i < iov_count; i++) {
+		size = I_MIN(iov[i].iov_len, avail);
+		buffer_append(sstream->buffer, iov[i].iov_base, size);
+		bytes_sent += size;
+		avail -= size;
+
+		if (size != iov[i].iov_len)
+			break;
+	}
+
+	sstream->ostream.ostream.offset += bytes_sent;
+	return bytes_sent;
+}
+
+static int o_stream_ssl_flush_buffer(struct ssl_ostream *sstream)
+{
+	struct ssl_iostream *ssl_io = sstream->ssl_io;
+	size_t pos = 0;
+	int ret = 1;
+
+	i_assert(!sstream->shutdown);
+
+	while (pos < sstream->buffer->used) {
+		/* we're writing plaintext data to OpenSSL, which it encrypts
+		   and writes to bio_int's buffer. ssl_iostream_bio_sync()
+		   reads it from there and adds to plain_output stream. */
+		ret = SSL_write(ssl_io->ssl,
+				CONST_PTR_OFFSET(sstream->buffer->data, pos),
+				sstream->buffer->used - pos);
+		if (ret <= 0) {
+			ret = openssl_iostream_handle_error(
+				ssl_io, ret, OPENSSL_IOSTREAM_SYNC_TYPE_WRITE,
+				"SSL_write");
+			if (ret < 0) {
+				io_stream_set_error(
+					&sstream->ostream.iostream,
+					"%s", ssl_io->last_error);
+				sstream->ostream.ostream.stream_errno = errno;
+				break;
+			}
+			if (ret == 0)
+				break;
+		} else {
+			pos += ret;
+			ret = openssl_iostream_bio_sync(
+				ssl_io, OPENSSL_IOSTREAM_SYNC_TYPE_WRITE);
+			if (ret < 0) {
+				i_assert(ssl_io->plain_stream_errstr != NULL &&
+					 ssl_io->plain_stream_errno != 0);
+				io_stream_set_error(
+					&sstream->ostream.iostream,
+					"%s", ssl_io->plain_stream_errstr);
+				sstream->ostream.ostream.stream_errno =
+					ssl_io->plain_stream_errno;
+				break;
+			}
+		}
+	}
+	buffer_delete(sstream->buffer, 0, pos);
+	return ret <= 0 ? ret : 1;
+}
+
+static int o_stream_ssl_flush(struct ostream_private *stream)
+{
+	struct ssl_ostream *sstream = (struct ssl_ostream *)stream;
+	struct ssl_iostream *ssl_io = sstream->ssl_io;
+	struct ostream *plain_output = ssl_io->plain_output;
+	int ret = 1;
+
+	if (!ssl_io->handshaked) {
+		if ((ret = ssl_iostream_handshake(ssl_io)) < 0) {
+			/* handshake failed */
+			i_assert(errno != 0);
+			io_stream_set_error(&stream->iostream,
+					    "%s", ssl_io->last_error);
+			stream->ostream.stream_errno = errno;
+			return ret;
+		}
+	}
+	if (ret > 0 &&
+	    openssl_iostream_bio_sync(
+		ssl_io, OPENSSL_IOSTREAM_SYNC_TYPE_HANDSHAKE) < 0) {
+		i_assert(ssl_io->plain_stream_errno != 0 &&
+			 ssl_io->plain_stream_errstr != NULL);
+		io_stream_set_error(&stream->iostream,
+				    "%s", ssl_io->plain_stream_errstr);
+		stream->ostream.stream_errno = ssl_io->plain_stream_errno;
+		return -1;
+	}
+
+	if (ret > 0 && sstream->buffer != NULL && sstream->buffer->used > 0) {
+		/* we can try to send some of our buffered data */
+		ret = o_stream_ssl_flush_buffer(sstream);
+	}
+
+	/* Stream is finished; shutdown the SSL write direction once our buffer
+	   is empty. */
+	if (stream->finished && !sstream->shutdown && ret >= 0 &&
+	    (sstream->buffer == NULL || sstream->buffer->used == 0)) {
+		sstream->shutdown = TRUE;
+		if (SSL_shutdown(ssl_io->ssl) < 0) {
+			io_stream_set_error(
+				&sstream->ostream.iostream, "%s",
+				t_strdup_printf("SSL_shutdown() failed: %s",
+						openssl_iostream_error()));
+			sstream->ostream.ostream.stream_errno = EIO;
+			ret = -1;
+		}
+	}
+
+	if (ret == 0 && ssl_io->want_read) {
+		/* we need to read more data until we can continue. */
+		o_stream_set_flush_pending(plain_output, FALSE);
+		ssl_io->ostream_flush_waiting_input = TRUE;
+		ret = 1;
+	}
+
+	if (ret <= 0)
+		return ret;
+
+	/* return 1 only when the output buffer is empty, which is what the
+	   caller expects. */
+	return o_stream_get_buffer_used_size(plain_output) == 0 ? 1 : 0;
+}
+
+static ssize_t
+o_stream_ssl_sendv(struct ostream_private *stream,
+		   const struct const_iovec *iov, unsigned int iov_count)
+{
+	struct ssl_ostream *sstream = (struct ssl_ostream *)stream;
+	size_t bytes_sent = 0;
+
+	i_assert(!sstream->shutdown);
+
+	bytes_sent = o_stream_ssl_buffer(sstream, iov, iov_count, bytes_sent);
+	if (sstream->ssl_io->handshaked &&
+	    sstream->buffer->used == bytes_sent) {
+		/* buffer was empty before calling this. try to write it
+		   immediately. */
+		if (o_stream_ssl_flush_buffer(sstream) < 0)
+			return -1;
+	}
+	return bytes_sent;
+}
+
+static void o_stream_ssl_switch_ioloop_to(struct ostream_private *stream,
+					  struct ioloop *ioloop)
+{
+	struct ssl_ostream *sstream = (struct ssl_ostream *)stream;
+
+	o_stream_switch_ioloop_to(sstream->ssl_io->plain_output, ioloop);
+}
+
+static int plain_flush_callback(struct ssl_ostream *sstream)
+{
+	struct ostream *ostream = &sstream->ostream.ostream;
+	int ret, ret2;
+
+	/* try to actually flush the pending data */
+	if ((ret = o_stream_flush(sstream->ssl_io->plain_output)) < 0)
+		return -1;
+
+	/* we may be able to copy more data, try it */
+	o_stream_ref(ostream);
+	if (sstream->ostream.callback != NULL)
+		ret2 = sstream->ostream.callback(sstream->ostream.context);
+	else
+		ret2 = o_stream_flush(&sstream->ostream.ostream);
+	if (ret2 == 0)
+		o_stream_set_flush_pending(sstream->ssl_io->plain_output, TRUE);
+	o_stream_unref(&ostream);
+	if (ret2 < 0)
+		return -1;
+	return ret > 0 && ret2 > 0 ? 1 : 0;
+}
+
+static size_t
+o_stream_ssl_get_buffer_used_size(const struct ostream_private *stream)
+{
+	const struct ssl_ostream *sstream = (const struct ssl_ostream *)stream;
+	BIO *bio = SSL_get_wbio(sstream->ssl_io->ssl);
+	size_t wbuf_avail = BIO_ctrl_get_write_guarantee(bio);
+	size_t wbuf_total_size = BIO_get_write_buf_size(bio, 0);
+	size_t buffer_used = (sstream->buffer == NULL ? 0 :
+			      sstream->buffer->used);
+	i_assert(wbuf_avail <= wbuf_total_size);
+	return buffer_used + (wbuf_total_size - wbuf_avail) +
+		o_stream_get_buffer_used_size(sstream->ssl_io->plain_output);
+}
+
+static size_t
+o_stream_ssl_get_buffer_avail_size(const struct ostream_private *stream)
+{
+	const struct ssl_ostream *sstream = (const struct ssl_ostream *)stream;
+
+	return get_buffer_avail_size(sstream);
+}
+
+static void
+o_stream_ssl_flush_pending(struct ostream_private *_stream, bool set)
+{
+	struct ssl_ostream *sstream = (struct ssl_ostream *)_stream;
+
+	o_stream_set_flush_pending(sstream->ssl_io->plain_output, set);
+}
+
+static void o_stream_ssl_set_max_buffer_size(struct iostream_private *_stream,
+					     size_t max_size)
+{
+	struct ssl_ostream *sstream = (struct ssl_ostream *)_stream;
+
+	sstream->ostream.max_buffer_size = max_size;
+	o_stream_set_max_buffer_size(sstream->ssl_io->plain_output, max_size);
+}
+
+struct ostream *openssl_o_stream_create_ssl(struct ssl_iostream *ssl_io)
+{
+	struct ssl_ostream *sstream;
+
+	ssl_io->refcount++;
+
+	/* When ostream is destroyed, it's flushed. With iostream-ssl the
+	   flushing requires both istream and ostream to be available. The
+	   istream is referenced here to make sure it's not destroyed before
+	   the ostream. */
+	i_assert(ssl_io->ssl_input != NULL);
+	i_stream_ref(ssl_io->ssl_input);
+
+	sstream = i_new(struct ssl_ostream, 1);
+	sstream->ssl_io = ssl_io;
+	sstream->ostream.max_buffer_size =
+		ssl_io->plain_output->real_stream->max_buffer_size;
+	sstream->ostream.iostream.close = o_stream_ssl_close;
+	sstream->ostream.iostream.destroy = o_stream_ssl_destroy;
+	sstream->ostream.sendv = o_stream_ssl_sendv;
+	sstream->ostream.flush = o_stream_ssl_flush;
+	sstream->ostream.switch_ioloop_to = o_stream_ssl_switch_ioloop_to;
+
+	sstream->ostream.get_buffer_used_size =
+		o_stream_ssl_get_buffer_used_size;
+	sstream->ostream.get_buffer_avail_size =
+		o_stream_ssl_get_buffer_avail_size;
+	sstream->ostream.flush_pending = o_stream_ssl_flush_pending;
+	sstream->ostream.iostream.set_max_buffer_size =
+		o_stream_ssl_set_max_buffer_size;
+
+	sstream->ostream.callback = ssl_io->plain_output->real_stream->callback;
+	sstream->ostream.context = ssl_io->plain_output->real_stream->context;
+	o_stream_set_flush_callback(ssl_io->plain_output,
+				    plain_flush_callback, sstream);
+
+	return o_stream_create(&sstream->ostream, NULL,
+			       o_stream_get_fd(ssl_io->plain_output));
+}
diff --git a/src/lib-ssl-iostream/test-iostream-ssl.c b/src/lib-ssl-iostream/test-iostream-ssl.c
new file mode 100644
index 0000000..b2533ac
--- /dev/null
+++ b/src/lib-ssl-iostream/test-iostream-ssl.c
@@ -0,0 +1,559 @@
+/* Copyright (c) 2018 Dovecot authors, see the included COPYING file */
+
+#include "test-lib.h"
+#include "buffer.h"
+#include "randgen.h"
+#include "istream.h"
+#include "ostream.h"
+#include "iostream-openssl.h"
+#include "iostream-ssl.h"
+#include "iostream-ssl-test.h"
+
+#include <sys/socket.h>
+
+#define MAX_SENT_BYTES 10000
+
+struct test_endpoint {
+	pool_t pool;
+	int fd;
+	const char *hostname;
+	const struct ssl_iostream_settings *set;
+	struct ssl_iostream_context *ctx;
+	struct ssl_iostream *iostream;
+	struct istream *input;
+	struct ostream *output;
+	struct io *io;
+	buffer_t *last_write;
+	ssize_t sent;
+	bool client;
+	bool failed;
+
+	struct test_endpoint *other;
+
+	bool finished:1;
+};
+
+static void send_output(struct test_endpoint *ep)
+{
+	ssize_t amt = i_rand_limit(10)+1;
+	char data[amt];
+	random_fill(data, amt);
+	buffer_append(ep->other->last_write, data, amt);
+	test_assert(o_stream_send(ep->output, data, amt) == amt);
+	ep->sent += amt;
+}
+
+static int flush_output(struct test_endpoint *ep, bool finish)
+{
+	int ret = (finish ?
+		   o_stream_finish(ep->output) : o_stream_flush(ep->output));
+	test_assert(ret >= 0);
+
+	if (ret > 0) {
+		if (finish)
+			ep->finished = TRUE;
+		if (ep->other->finished)
+			io_loop_stop(current_ioloop);
+	}
+	return ret;
+}
+
+static void handshake_input_callback(struct test_endpoint *ep)
+{
+	if (ep->failed)
+		return;
+	if (ssl_iostream_is_handshaked(ep->iostream)) {
+		if (ssl_iostream_is_handshaked(ep->other->iostream))
+			io_loop_stop(current_ioloop);
+		return;
+	}
+	if (ssl_iostream_handshake(ep->iostream) < 0) {
+		ep->failed = TRUE;
+		io_loop_stop(current_ioloop);
+	}
+}
+
+static int bufsize_flush_callback(struct test_endpoint *ep)
+{
+	io_loop_stop(current_ioloop);
+	return flush_output(ep, FALSE);
+}
+
+static int bufsize_finish_callback(struct test_endpoint *ep)
+{
+	return flush_output(ep, TRUE);
+}
+
+static void bufsize_input_callback(struct test_endpoint *ep)
+{
+	const unsigned char *data;
+	size_t size, wanted = i_rand_limit(512);
+
+	io_loop_stop(current_ioloop);
+	if (wanted == 0)
+		return;
+
+	test_assert(i_stream_read_bytes(ep->input, &data, &size, wanted) > -1);
+	i_stream_skip(ep->input, I_MIN(size, wanted));
+}
+
+static void bufsize_discard_callback(struct test_endpoint *ep)
+{
+	const unsigned char *data;
+	size_t size;
+
+	test_assert(i_stream_read_bytes(ep->input, &data, &size, 1) > -1 ||
+		    ep->input->stream_errno == 0);
+	i_stream_skip(ep->input, size);
+}
+
+static int small_packets_flush_callback(struct test_endpoint *ep)
+{
+	return flush_output(ep, FALSE);
+}
+
+static void small_packets_input_callback(struct test_endpoint *ep)
+{
+	const unsigned char *data;
+	size_t size, wanted = i_rand_limit(10);
+	int ret;
+
+	if (wanted == 0) {
+		i_stream_set_input_pending(ep->input, TRUE);
+		return;
+	}
+
+	size = 0;
+	test_assert((ret = i_stream_read_bytes(ep->input, &data, &size, wanted)) > -1 ||
+		    ep->input->stream_errno == 0);
+
+	if (size > wanted)
+		i_stream_set_input_pending(ep->input, TRUE);
+
+	size = I_MIN(size, wanted);
+
+	i_stream_skip(ep->input, size);
+	if (size > 0) {
+		test_assert(ep->last_write->used >= size);
+		if (ep->last_write->used >= size) {
+			test_assert(memcmp(ep->last_write->data, data, size) == 0);
+			/* remove the data that was wanted */
+			buffer_delete(ep->last_write, 0, size);
+		}
+	}
+
+	if (ep->sent > MAX_SENT_BYTES)
+		(void)flush_output(ep, TRUE);
+	else
+		send_output(ep);
+}
+
+static struct test_endpoint *
+create_test_endpoint(int fd, const struct ssl_iostream_settings *set)
+{
+	pool_t pool = pool_alloconly_create("ssl endpoint", 2048);
+	struct test_endpoint *ep = p_new(pool, struct test_endpoint, 1);
+	ep->pool = pool;
+	ep->fd = fd;
+	ep->input = i_stream_create_fd(ep->fd, 512);
+	ep->output = o_stream_create_fd(ep->fd, 1024);
+	o_stream_uncork(ep->output);
+	ep->set = ssl_iostream_settings_dup(pool, set);
+	ep->last_write = buffer_create_dynamic(pool, 1024);
+	return ep;
+}
+
+static void destroy_test_endpoint(struct test_endpoint **_ep)
+{
+	struct test_endpoint *ep = *_ep;
+	_ep = NULL;
+
+	io_remove(&ep->io);
+
+	i_stream_unref(&ep->input);
+	o_stream_unref(&ep->output);
+	ssl_iostream_destroy(&ep->iostream);
+	i_close_fd(&ep->fd);
+	if (ep->ctx != NULL)
+		ssl_iostream_context_unref(&ep->ctx);
+	pool_unref(&ep->pool);
+}
+
+static int test_iostream_ssl_handshake_real(struct ssl_iostream_settings *server_set,
+					    struct ssl_iostream_settings *client_set,
+					    const char *hostname)
+{
+	const char *error;
+	struct test_endpoint *server, *client;
+	int fd[2], ret = 0;
+
+	if (socketpair(AF_UNIX, SOCK_STREAM, 0, fd) < 0)
+		i_fatal("socketpair() failed: %m");
+	fd_set_nonblock(fd[0], TRUE);
+	fd_set_nonblock(fd[1], TRUE);
+
+	server = create_test_endpoint(fd[0], server_set);
+	client = create_test_endpoint(fd[1], client_set);
+	client->hostname = hostname;
+	client->client = TRUE;
+
+	server->other = client;
+	client->other = server;
+
+	if (ssl_iostream_context_init_server(server->set, &server->ctx,
+					     &error) < 0) {
+		i_error("server: %s", error);
+		destroy_test_endpoint(&client);
+		destroy_test_endpoint(&server);
+		return -1;
+	}
+	if (ssl_iostream_context_init_client(client->set, &client->ctx,
+					     &error) < 0) {
+		i_error("client: %s", error);
+		destroy_test_endpoint(&client);
+		destroy_test_endpoint(&server);
+		return -1;
+	}
+
+	if (io_stream_create_ssl_server(server->ctx, server->set,
+					&server->input, &server->output,
+					&server->iostream, &error) != 0) {
+		ret = -1;
+	}
+
+	if (io_stream_create_ssl_client(client->ctx, client->hostname, client->set,
+					&client->input, &client->output,
+					&client->iostream, &error) != 0) {
+		ret = -1;
+	}
+
+	client->io = io_add_istream(client->input, handshake_input_callback, client);
+	server->io = io_add_istream(server->input, handshake_input_callback, server);
+
+	if (ssl_iostream_handshake(client->iostream) < 0)
+		return -1;
+
+	io_loop_run(current_ioloop);
+
+	if (client->failed || server->failed)
+		ret = -1;
+
+	if (ssl_iostream_has_handshake_failed(client->iostream)) {
+		i_error("client: %s", ssl_iostream_get_last_error(client->iostream));
+		ret = -1;
+	} else if (ssl_iostream_has_handshake_failed(server->iostream)) {
+		i_error("server: %s", ssl_iostream_get_last_error(server->iostream));
+		ret = -1;
+	/* check hostname */
+	} else if (client->hostname != NULL &&
+	    !client->set->allow_invalid_cert &&
+	    ssl_iostream_check_cert_validity(client->iostream, client->hostname,
+					     &error) != 0) {
+		i_error("client(%s): %s", client->hostname, error);
+		ret = -1;
+	/* client cert */
+	} else if (server->set->verify_remote_cert &&
+	    ssl_iostream_check_cert_validity(server->iostream, NULL, &error) != 0) {
+		i_error("server: %s", error);
+		ret = -1;
+	}
+
+	i_stream_unref(&server->input);
+	o_stream_unref(&server->output);
+	i_stream_unref(&client->input);
+	o_stream_unref(&client->output);
+
+	destroy_test_endpoint(&client);
+	destroy_test_endpoint(&server);
+
+	return ret;
+}
+
+static void test_iostream_ssl_handshake(void)
+{
+	struct ssl_iostream_settings server_set, client_set;
+	struct ioloop *ioloop;
+	int idx = 0;
+
+	test_begin("ssl: handshake");
+
+	ioloop = io_loop_create();
+
+	/* allow invalid cert, connect to localhost */
+	ssl_iostream_test_settings_server(&server_set);
+	ssl_iostream_test_settings_client(&client_set);
+	client_set.allow_invalid_cert = TRUE;
+	test_assert_idx(test_iostream_ssl_handshake_real(&server_set, &client_set,
+							 "localhost") == 0, idx);
+	idx++;
+
+	/* allow invalid cert, connect to failhost */
+	ssl_iostream_test_settings_server(&server_set);
+	ssl_iostream_test_settings_client(&client_set);
+	client_set.allow_invalid_cert = TRUE;
+	test_assert_idx(test_iostream_ssl_handshake_real(&server_set, &client_set,
+							 "failhost") == 0, idx);
+	idx++;
+
+	/* verify remote cert */
+	ssl_iostream_test_settings_server(&server_set);
+	ssl_iostream_test_settings_client(&client_set);
+	client_set.verify_remote_cert = TRUE;
+	test_assert_idx(test_iostream_ssl_handshake_real(&server_set, &client_set,
+							 "127.0.0.1") == 0, idx);
+	idx++;
+
+	/* verify remote cert, missing hostname */
+	ssl_iostream_test_settings_server(&server_set);
+	ssl_iostream_test_settings_client(&client_set);
+	client_set.verify_remote_cert = TRUE;
+	test_expect_error_string("client: SSL certificate doesn't "
+				 "match expected host name failhost");
+	test_assert_idx(test_iostream_ssl_handshake_real(&server_set, &client_set,
+							 "failhost") != 0, idx);
+	idx++;
+
+	/* verify remote cert, missing CA */
+	ssl_iostream_test_settings_server(&server_set);
+	ssl_iostream_test_settings_client(&client_set);
+	client_set.verify_remote_cert = TRUE;
+	client_set.ca = NULL;
+	test_expect_error_string("client: Received invalid SSL certificate");
+	test_assert_idx(test_iostream_ssl_handshake_real(&server_set, &client_set,
+							 "127.0.0.1") != 0, idx);
+	idx++;
+
+	/* verify remote cert, require CRL */
+	ssl_iostream_test_settings_server(&server_set);
+	ssl_iostream_test_settings_client(&client_set);
+	client_set.verify_remote_cert = TRUE;
+	client_set.skip_crl_check = FALSE;
+	test_expect_error_string("client: Received invalid SSL certificate");
+	test_assert_idx(test_iostream_ssl_handshake_real(&server_set, &client_set,
+							 "127.0.0.1") != 0, idx);
+	idx++;
+
+	/* missing server credentials */
+	ssl_iostream_test_settings_server(&server_set);
+	server_set.cert.key = NULL;
+	ssl_iostream_test_settings_client(&client_set);
+	client_set.verify_remote_cert = TRUE;
+	test_expect_error_string("client(failhost): SSL certificate not received");
+	test_assert_idx(test_iostream_ssl_handshake_real(&server_set, &client_set,
+							 "failhost") != 0, idx);
+	idx++;
+	ssl_iostream_test_settings_server(&server_set);
+	server_set.cert.cert = NULL;
+	ssl_iostream_test_settings_client(&client_set);
+	client_set.verify_remote_cert = TRUE;
+	test_expect_error_string("client(failhost): SSL certificate not received");
+	test_assert_idx(test_iostream_ssl_handshake_real(&server_set, &client_set,
+							 "failhost") != 0, idx);
+	idx++;
+
+	/* invalid client credentials: missing credentials */
+	ssl_iostream_test_settings_server(&server_set);
+	ssl_iostream_test_settings_client(&client_set);
+	client_set.verify_remote_cert = TRUE;
+	server_set.verify_remote_cert = TRUE;
+	server_set.ca = client_set.ca;
+	test_expect_error_string("server: SSL certificate not received");
+	test_assert_idx(test_iostream_ssl_handshake_real(&server_set, &client_set,
+							 "127.0.0.1") != 0, idx);
+	idx++;
+
+	/* invalid client credentials: incorrect extended usage */
+	ssl_iostream_test_settings_server(&server_set);
+	ssl_iostream_test_settings_client(&client_set);
+	client_set.verify_remote_cert = TRUE;
+	server_set.verify_remote_cert = TRUE;
+	server_set.ca = client_set.ca;
+	client_set.cert = server_set.cert;
+	test_expect_error_string("server: SSL_accept() failed: error:");
+	test_assert_idx(test_iostream_ssl_handshake_real(&server_set, &client_set,
+							 "127.0.0.1") != 0, idx);
+	idx++;
+
+	io_loop_destroy(&ioloop);
+
+	test_end();
+}
+
+static void test_iostream_ssl_get_buffer_avail_size(void)
+{
+	struct ssl_iostream_settings set;
+	struct test_endpoint *server, *client;
+	struct ioloop *ioloop;
+	int fd[2];
+	const char *error;
+
+	test_begin("ssl: o_stream_get_buffer_avail_size");
+
+	if (socketpair(AF_UNIX, SOCK_STREAM, 0, fd) < 0)
+		i_fatal("socketpair() failed: %m");
+	fd_set_nonblock(fd[0], TRUE);
+	fd_set_nonblock(fd[1], TRUE);
+
+	ioloop = io_loop_create();
+
+	ssl_iostream_test_settings_server(&set);
+	server = create_test_endpoint(fd[0], &set);
+	ssl_iostream_test_settings_client(&set);
+	set.allow_invalid_cert = TRUE;
+	client = create_test_endpoint(fd[1], &set);
+	client->client = TRUE;
+
+	client->other = server;
+	server->other = client;
+
+	test_assert(ssl_iostream_context_init_server(server->set, &server->ctx,
+		    &error) == 0);
+	test_assert(ssl_iostream_context_init_client(client->set, &client->ctx,
+		    &error) == 0);
+
+	test_assert(io_stream_create_ssl_server(server->ctx, server->set,
+						&server->input, &server->output,
+						&server->iostream, &error) == 0);
+	test_assert(io_stream_create_ssl_client(client->ctx, "localhost", client->set,
+						&client->input, &client->output,
+						&client->iostream, &error) == 0);
+
+	o_stream_set_flush_callback(server->output, bufsize_flush_callback, server);
+	o_stream_set_flush_callback(client->output, bufsize_flush_callback, client);
+
+	server->io = io_add_istream(server->input, bufsize_input_callback, server);
+	client->io = io_add_istream(client->input, bufsize_input_callback, client);
+
+	test_assert(ssl_iostream_handshake(client->iostream) == 0);
+	test_assert(ssl_iostream_handshake(server->iostream) == 0);
+
+	for (unsigned int i = 0; i < 100000 && !test_has_failed(); i++) {
+		size_t avail = o_stream_get_buffer_avail_size(server->output);
+		if (avail > 0) {
+			void *buf = i_malloc(avail);
+			random_fill(buf, avail);
+			test_assert(o_stream_send(server->output, buf, avail) ==
+				    (ssize_t)avail);
+			i_free(buf);
+		}
+		avail = o_stream_get_buffer_avail_size(client->output);
+		if (avail > 0) {
+			void *buf = i_malloc(avail);
+			random_fill(buf, avail);
+			test_assert(o_stream_send(client->output, buf, avail) ==
+				    (ssize_t)avail);
+			i_free(buf);
+		}
+		io_loop_run(ioloop);
+	}
+
+	io_remove(&server->io);
+	io_remove(&client->io);
+	o_stream_set_flush_callback(server->output, bufsize_finish_callback, server);
+	o_stream_set_flush_callback(client->output, bufsize_finish_callback, client);
+	server->io = io_add_istream(server->input, bufsize_discard_callback, server);
+	client->io = io_add_istream(client->input, bufsize_discard_callback, client);
+	o_stream_set_flush_pending(server->output, TRUE);
+	o_stream_set_flush_pending(client->output, TRUE);
+	io_loop_run(ioloop);
+
+	i_stream_unref(&server->input);
+	o_stream_unref(&server->output);
+	i_stream_unref(&client->input);
+	o_stream_unref(&client->output);
+
+	destroy_test_endpoint(&client);
+	destroy_test_endpoint(&server);
+
+	io_loop_destroy(&ioloop);
+
+	test_end();
+}
+
+static void test_iostream_ssl_small_packets(void)
+{
+	struct ssl_iostream_settings set;
+	struct test_endpoint *server, *client;
+	struct ioloop *ioloop;
+	int fd[2];
+	const char *error;
+
+	test_begin("ssl: small packets");
+
+	if (socketpair(AF_UNIX, SOCK_STREAM, 0, fd) < 0)
+		i_fatal("socketpair() failed: %m");
+	fd_set_nonblock(fd[0], TRUE);
+	fd_set_nonblock(fd[1], TRUE);
+
+	ioloop = io_loop_create();
+
+	ssl_iostream_test_settings_server(&set);
+	server = create_test_endpoint(fd[0], &set);
+	ssl_iostream_test_settings_client(&set);
+	set.allow_invalid_cert = TRUE;
+	client = create_test_endpoint(fd[1], &set);
+	client->client = TRUE;
+
+	test_assert(ssl_iostream_context_init_server(server->set, &server->ctx,
+		    &error) == 0);
+	test_assert(ssl_iostream_context_init_client(client->set, &client->ctx,
+		    &error) == 0);
+
+	client->other = server;
+	server->other = client;
+
+	test_assert(io_stream_create_ssl_server(server->ctx, server->set,
+						&server->input, &server->output,
+						&server->iostream, &error) == 0);
+	test_assert(io_stream_create_ssl_client(client->ctx, "localhost", client->set,
+						&client->input, &client->output,
+						&client->iostream, &error) == 0);
+
+	o_stream_set_flush_callback(server->output, small_packets_flush_callback,
+				    server);
+	o_stream_set_flush_callback(client->output, small_packets_flush_callback,
+				    client);
+
+	server->io = io_add_istream(server->input, small_packets_input_callback,
+				    server);
+	client->io = io_add_istream(client->input, small_packets_input_callback,
+				    client);
+
+	test_assert(ssl_iostream_handshake(client->iostream) == 0);
+	test_assert(ssl_iostream_handshake(server->iostream) == 0);
+
+	struct timeout *to = timeout_add(5000, io_loop_stop, ioloop);
+
+	io_loop_run(ioloop);
+
+	timeout_remove(&to);
+
+	test_assert(server->sent > MAX_SENT_BYTES ||
+		    client->sent > MAX_SENT_BYTES);
+
+	i_stream_unref(&server->input);
+	o_stream_unref(&server->output);
+	i_stream_unref(&client->input);
+	o_stream_unref(&client->output);
+
+	destroy_test_endpoint(&server);
+	destroy_test_endpoint(&client);
+
+	io_loop_destroy(&ioloop);
+
+	test_end();
+}
+
+int main(void)
+{
+	static void (*const test_functions[])(void) = {
+		test_iostream_ssl_handshake,
+		test_iostream_ssl_get_buffer_avail_size,
+		test_iostream_ssl_small_packets,
+		NULL
+	};
+	ssl_iostream_openssl_init();
+	int ret = test_run(test_functions);
+	ssl_iostream_openssl_deinit();
+	return ret;
+}